internal/reflectlite: lite version of reflect package

to be used by errors package for checking assignability
and setting error values in As.

Updates #29934.

Change-Id: I8c1d02a2c6efa0919d54b286cfe8b4edc26da059
Reviewed-on: https://go-review.googlesource.com/c/161759
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/go/build/deps_test.go

@@ -46,6 +46,7 @@ var pkgDeps = map[string][]string{
 	"unsafe":                  {},
 	"internal/cpu":            {},
 	"internal/bytealg":        {"unsafe", "internal/cpu"},
+	"internal/reflectlite":    {"runtime", "unsafe"},
 
 	"L0": {
 		"errors",
@@ -57,6 +58,7 @@ var pkgDeps = map[string][]string{
 		"unsafe",
 		"internal/cpu",
 		"internal/bytealg",
+		"internal/reflectlite",
 	},
 
 	// L1 adds simple functions and strings processing,

src/internal/reflectlite/asm.s

@@ -0,0 +1,5 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Trigger build without complete flag.

src/internal/reflectlite/export_test.go

@@ -0,0 +1,115 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflectlite
+
+import (
+	"unsafe"
+)
+
+// Field returns the i'th field of the struct v.
+// It panics if v's Kind is not Struct or i is out of range.
+func Field(v Value, i int) Value {
+	if v.kind() != Struct {
+		panic(&ValueError{"reflect.Value.Field", v.kind()})
+	}
+	tt := (*structType)(unsafe.Pointer(v.typ))
+	if uint(i) >= uint(len(tt.fields)) {
+		panic("reflect: Field index out of range")
+	}
+	field := &tt.fields[i]
+	typ := field.typ
+
+	// Inherit permission bits from v, but clear flagEmbedRO.
+	fl := v.flag&(flagStickyRO|flagIndir|flagAddr) | flag(typ.Kind())
+	// Using an unexported field forces flagRO.
+	if !field.name.isExported() {
+		if field.embedded() {
+			fl |= flagEmbedRO
+		} else {
+			fl |= flagStickyRO
+		}
+	}
+	// Either flagIndir is set and v.ptr points at struct,
+	// or flagIndir is not set and v.ptr is the actual struct data.
+	// In the former case, we want v.ptr + offset.
+	// In the latter case, we must have field.offset = 0,
+	// so v.ptr + field.offset is still the correct address.
+	ptr := add(v.ptr, field.offset(), "same as non-reflect &v.field")
+	return Value{typ, ptr, fl}
+}
+
+func TField(typ Type, i int) Type {
+	t := typ.(*rtype)
+	if t.Kind() != Struct {
+		panic("reflect: Field of non-struct type")
+	}
+	tt := (*structType)(unsafe.Pointer(t))
+
+	return StructFieldType(tt, i)
+}
+
+// Field returns the i'th struct field.
+func StructFieldType(t *structType, i int) Type {
+	if i < 0 || i >= len(t.fields) {
+		panic("reflect: Field index out of bounds")
+	}
+	p := &t.fields[i]
+	return toType(p.typ)
+}
+
+// Zero returns a Value representing the zero value for the specified type.
+// The result is different from the zero value of the Value struct,
+// which represents no value at all.
+// For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0.
+// The returned value is neither addressable nor settable.
+func Zero(typ Type) Value {
+	if typ == nil {
+		panic("reflect: Zero(nil)")
+	}
+	t := typ.(*rtype)
+	fl := flag(t.Kind())
+	if ifaceIndir(t) {
+		return Value{t, unsafe_New(t), fl | flagIndir}
+	}
+	return Value{t, nil, fl}
+}
+
+// ToInterface returns v's current value as an interface{}.
+// It is equivalent to:
+//	var i interface{} = (v's underlying value)
+// It panics if the Value was obtained by accessing
+// unexported struct fields.
+func ToInterface(v Value) (i interface{}) {
+	return valueInterface(v)
+}
+
+type EmbedWithUnexpMeth struct{}
+
+func (EmbedWithUnexpMeth) f() {}
+
+type pinUnexpMeth interface {
+	f()
+}
+
+var pinUnexpMethI = pinUnexpMeth(EmbedWithUnexpMeth{})
+
+func FirstMethodNameBytes(t Type) *byte {
+	_ = pinUnexpMethI
+
+	ut := t.uncommon()
+	if ut == nil {
+		panic("type has no methods")
+	}
+	m := ut.methods()[0]
+	mname := t.(*rtype).nameOff(m.name)
+	if *mname.data(0, "name flag field")&(1<<2) == 0 {
+		panic("method name does not have pkgPath *string")
+	}
+	return mname.bytes
+}
+
+type Buffer struct {
+	buf []byte
+}

src/internal/reflectlite/set_test.go

@@ -0,0 +1,92 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflectlite_test
+
+import (
+	"bytes"
+	"go/ast"
+	"go/token"
+	. "internal/reflectlite"
+	"io"
+	"testing"
+)
+
+func TestImplicitSetConversion(t *testing.T) {
+	// Assume TestImplicitMapConversion covered the basics.
+	// Just make sure conversions are being applied at all.
+	var r io.Reader
+	b := new(bytes.Buffer)
+	rv := ValueOf(&r).Elem()
+	rv.Set(ValueOf(b))
+	if r != b {
+		t.Errorf("after Set: r=%T(%v)", r, r)
+	}
+}
+
+var implementsTests = []struct {
+	x interface{}
+	t interface{}
+	b bool
+}{
+	{new(*bytes.Buffer), new(io.Reader), true},
+	{new(bytes.Buffer), new(io.Reader), false},
+	{new(*bytes.Buffer), new(io.ReaderAt), false},
+	{new(*ast.Ident), new(ast.Expr), true},
+	{new(*notAnExpr), new(ast.Expr), false},
+	{new(*ast.Ident), new(notASTExpr), false},
+	{new(notASTExpr), new(ast.Expr), false},
+	{new(ast.Expr), new(notASTExpr), false},
+	{new(*notAnExpr), new(notASTExpr), true},
+}
+
+type notAnExpr struct{}
+
+func (notAnExpr) Pos() token.Pos { return token.NoPos }
+func (notAnExpr) End() token.Pos { return token.NoPos }
+func (notAnExpr) exprNode()      {}
+
+type notASTExpr interface {
+	Pos() token.Pos
+	End() token.Pos
+	exprNode()
+}
+
+func TestImplements(t *testing.T) {
+	for _, tt := range implementsTests {
+		xv := TypeOf(tt.x).Elem()
+		xt := TypeOf(tt.t).Elem()
+		if b := xv.Implements(xt); b != tt.b {
+			t.Errorf("(%s).Implements(%s) = %v, want %v", TypeString(xv), TypeString(xt), b, tt.b)
+		}
+	}
+}
+
+var assignableTests = []struct {
+	x interface{}
+	t interface{}
+	b bool
+}{
+	{new(chan int), new(<-chan int), true},
+	{new(<-chan int), new(chan int), false},
+	{new(*int), new(IntPtr), true},
+	{new(IntPtr), new(*int), true},
+	{new(IntPtr), new(IntPtr1), false},
+	{new(Ch), new(<-chan interface{}), true},
+	// test runs implementsTests too
+}
+
+type IntPtr *int
+type IntPtr1 *int
+type Ch <-chan interface{}
+
+func TestAssignableTo(t *testing.T) {
+	for i, tt := range append(assignableTests, implementsTests...) {
+		xv := TypeOf(tt.x).Elem()
+		xt := TypeOf(tt.t).Elem()
+		if b := xv.AssignableTo(xt); b != tt.b {
+			t.Errorf("%d:AssignableTo: got %v, want %v", i, b, tt.b)
+		}
+	}
+}

src/internal/reflectlite/tostring_test.go

@@ -0,0 +1,98 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Formatting of reflection types and values for debugging.
+// Not defined as methods so they do not need to be linked into most binaries;
+// the functions are not used by the library itself, only in tests.
+
+package reflectlite_test
+
+import (
+	. "internal/reflectlite"
+	"reflect"
+	"strconv"
+)
+
+// valueToString returns a textual representation of the reflection value val.
+// For debugging only.
+func valueToString(v Value) string {
+	return valueToStringImpl(reflect.ValueOf(ToInterface(v)))
+}
+
+func valueToStringImpl(val reflect.Value) string {
+	var str string
+	if !val.IsValid() {
+		return "<zero Value>"
+	}
+	typ := val.Type()
+	switch val.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return strconv.FormatInt(val.Int(), 10)
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return strconv.FormatUint(val.Uint(), 10)
+	case reflect.Float32, reflect.Float64:
+		return strconv.FormatFloat(val.Float(), 'g', -1, 64)
+	case reflect.Complex64, reflect.Complex128:
+		c := val.Complex()
+		return strconv.FormatFloat(real(c), 'g', -1, 64) + "+" + strconv.FormatFloat(imag(c), 'g', -1, 64) + "i"
+	case reflect.String:
+		return val.String()
+	case reflect.Bool:
+		if val.Bool() {
+			return "true"
+		} else {
+			return "false"
+		}
+	case reflect.Ptr:
+		v := val
+		str = typ.String() + "("
+		if v.IsNil() {
+			str += "0"
+		} else {
+			str += "&" + valueToStringImpl(v.Elem())
+		}
+		str += ")"
+		return str
+	case reflect.Array, reflect.Slice:
+		v := val
+		str += typ.String()
+		str += "{"
+		for i := 0; i < v.Len(); i++ {
+			if i > 0 {
+				str += ", "
+			}
+			str += valueToStringImpl(v.Index(i))
+		}
+		str += "}"
+		return str
+	case reflect.Map:
+		str += typ.String()
+		str += "{"
+		str += "<can't iterate on maps>"
+		str += "}"
+		return str
+	case reflect.Chan:
+		str = typ.String()
+		return str
+	case reflect.Struct:
+		t := typ
+		v := val
+		str += t.String()
+		str += "{"
+		for i, n := 0, v.NumField(); i < n; i++ {
+			if i > 0 {
+				str += ", "
+			}
+			str += valueToStringImpl(v.Field(i))
+		}
+		str += "}"
+		return str
+	case reflect.Interface:
+		return typ.String() + "(" + valueToStringImpl(val.Elem()) + ")"
+	case reflect.Func:
+		return typ.String() + "(arg)"
+	default:
+		panic("valueToString: can't print type " + typ.String())
+	}
+}

src/internal/reflectlite/type.go

@@ -0,0 +1,904 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package reflectlite implements lightweight version of reflect, not using
+// any package except for "runtime" and "unsafe".
+package reflectlite
+
+import (
+	"unsafe"
+)
+
+// Type is the representation of a Go type.
+//
+// Not all methods apply to all kinds of types. Restrictions,
+// if any, are noted in the documentation for each method.
+// Use the Kind method to find out the kind of type before
+// calling kind-specific methods. Calling a method
+// inappropriate to the kind of type causes a run-time panic.
+//
+// Type values are comparable, such as with the == operator,
+// so they can be used as map keys.
+// Two Type values are equal if they represent identical types.
+type Type interface {
+	// Methods applicable to all types.
+
+	// Name returns the type's name within its package for a defined type.
+	// For other (non-defined) types it returns the empty string.
+	Name() string
+
+	// PkgPath returns a defined type's package path, that is, the import path
+	// that uniquely identifies the package, such as "encoding/base64".
+	// If the type was predeclared (string, error) or not defined (*T, struct{},
+	// []int, or A where A is an alias for a non-defined type), the package path
+	// will be the empty string.
+	PkgPath() string
+
+	// Kind returns the specific kind of this type.
+	Kind() Kind
+
+	// Implements reports whether the type implements the interface type u.
+	Implements(u Type) bool
+
+	// AssignableTo reports whether a value of the type is assignable to type u.
+	AssignableTo(u Type) bool
+
+	// Elem returns a type's element type.
+	// It panics if the type's Kind is not Ptr.
+	Elem() Type
+
+	common() *rtype
+	uncommon() *uncommonType
+}
+
+/*
+ * These data structures are known to the compiler (../../cmd/internal/gc/reflect.go).
+ * A few are known to ../runtime/type.go to convey to debuggers.
+ * They are also known to ../runtime/type.go.
+ */
+
+// A Kind represents the specific kind of type that a Type represents.
+// The zero Kind is not a valid kind.
+type Kind uint
+
+const (
+	Invalid Kind = iota
+	Bool
+	Int
+	Int8
+	Int16
+	Int32
+	Int64
+	Uint
+	Uint8
+	Uint16
+	Uint32
+	Uint64
+	Uintptr
+	Float32
+	Float64
+	Complex64
+	Complex128
+	Array
+	Chan
+	Func
+	Interface
+	Map
+	Ptr
+	Slice
+	String
+	Struct
+	UnsafePointer
+)
+
+// tflag is used by an rtype to signal what extra type information is
+// available in the memory directly following the rtype value.
+//
+// tflag values must be kept in sync with copies in:
+//	cmd/compile/internal/gc/reflect.go
+//	cmd/link/internal/ld/decodesym.go
+//	runtime/type.go
+type tflag uint8
+
+const (
+	// tflagUncommon means that there is a pointer, *uncommonType,
+	// just beyond the outer type structure.
+	//
+	// For example, if t.Kind() == Struct and t.tflag&tflagUncommon != 0,
+	// then t has uncommonType data and it can be accessed as:
+	//
+	//	type tUncommon struct {
+	//		structType
+	//		u uncommonType
+	//	}
+	//	u := &(*tUncommon)(unsafe.Pointer(t)).u
+	tflagUncommon tflag = 1 << 0
+
+	// tflagExtraStar means the name in the str field has an
+	// extraneous '*' prefix. This is because for most types T in
+	// a program, the type *T also exists and reusing the str data
+	// saves binary size.
+	tflagExtraStar tflag = 1 << 1
+
+	// tflagNamed means the type has a name.
+	tflagNamed tflag = 1 << 2
+)
+
+// rtype is the common implementation of most values.
+// It is embedded in other struct types.
+//
+// rtype must be kept in sync with ../runtime/type.go:/^type._type.
+type rtype struct {
+	size       uintptr
+	ptrdata    uintptr  // number of bytes in the type that can contain pointers
+	hash       uint32   // hash of type; avoids computation in hash tables
+	tflag      tflag    // extra type information flags
+	align      uint8    // alignment of variable with this type
+	fieldAlign uint8    // alignment of struct field with this type
+	kind       uint8    // enumeration for C
+	alg        *typeAlg // algorithm table
+	gcdata     *byte    // garbage collection data
+	str        nameOff  // string form
+	ptrToThis  typeOff  // type for pointer to this type, may be zero
+}
+
+// a copy of runtime.typeAlg
+type typeAlg struct {
+	// function for hashing objects of this type
+	// (ptr to object, seed) -> hash
+	hash func(unsafe.Pointer, uintptr) uintptr
+	// function for comparing objects of this type
+	// (ptr to object A, ptr to object B) -> ==?
+	equal func(unsafe.Pointer, unsafe.Pointer) bool
+}
+
+// Method on non-interface type
+type method struct {
+	name nameOff // name of method
+	mtyp typeOff // method type (without receiver)
+	ifn  textOff // fn used in interface call (one-word receiver)
+	tfn  textOff // fn used for normal method call
+}
+
+// uncommonType is present only for defined types or types with methods
+// (if T is a defined type, the uncommonTypes for T and *T have methods).
+// Using a pointer to this struct reduces the overall size required
+// to describe a non-defined type with no methods.
+type uncommonType struct {
+	pkgPath nameOff // import path; empty for built-in types like int, string
+	mcount  uint16  // number of methods
+	xcount  uint16  // number of exported methods
+	moff    uint32  // offset from this uncommontype to [mcount]method
+	_       uint32  // unused
+}
+
+// chanDir represents a channel type's direction.
+type chanDir int
+
+const (
+	recvDir chanDir             = 1 << iota // <-chan
+	sendDir                                 // chan<-
+	bothDir = recvDir | sendDir             // chan
+)
+
+// arrayType represents a fixed array type.
+type arrayType struct {
+	rtype
+	elem  *rtype // array element type
+	slice *rtype // slice type
+	len   uintptr
+}
+
+// chanType represents a channel type.
+type chanType struct {
+	rtype
+	elem *rtype  // channel element type
+	dir  uintptr // channel direction (chanDir)
+}
+
+// funcType represents a function type.
+//
+// A *rtype for each in and out parameter is stored in an array that
+// directly follows the funcType (and possibly its uncommonType). So
+// a function type with one method, one input, and one output is:
+//
+//	struct {
+//		funcType
+//		uncommonType
+//		[2]*rtype    // [0] is in, [1] is out
+//	}
+type funcType struct {
+	rtype
+	inCount  uint16
+	outCount uint16 // top bit is set if last input parameter is ...
+}
+
+// imethod represents a method on an interface type
+type imethod struct {
+	name nameOff // name of method
+	typ  typeOff // .(*FuncType) underneath
+}
+
+// interfaceType represents an interface type.
+type interfaceType struct {
+	rtype
+	pkgPath name      // import path
+	methods []imethod // sorted by hash
+}
+
+// mapType represents a map type.
+type mapType struct {
+	rtype
+	key        *rtype // map key type
+	elem       *rtype // map element (value) type
+	keysize    uint8  // size of key slot
+	valuesize  uint8  // size of value slot
+	bucketsize uint16 // size of bucket
+	flags      uint32
+}
+
+// ptrType represents a pointer type.
+type ptrType struct {
+	rtype
+	elem *rtype // pointer element (pointed at) type
+}
+
+// sliceType represents a slice type.
+type sliceType struct {
+	rtype
+	elem *rtype // slice element type
+}
+
+// Struct field
+type structField struct {
+	name        name    // name is always non-empty
+	typ         *rtype  // type of field
+	offsetEmbed uintptr // byte offset of field<<1 | isEmbedded
+}
+
+func (f *structField) offset() uintptr {
+	return f.offsetEmbed >> 1
+}
+
+func (f *structField) embedded() bool {
+	return f.offsetEmbed&1 != 0
+}
+
+// structType represents a struct type.
+type structType struct {
+	rtype
+	pkgPath name
+	fields  []structField // sorted by offset
+}
+
+// name is an encoded type name with optional extra data.
+//
+// The first byte is a bit field containing:
+//
+//	1<<0 the name is exported
+//	1<<1 tag data follows the name
+//	1<<2 pkgPath nameOff follows the name and tag
+//
+// The next two bytes are the data length:
+//
+//	 l := uint16(data[1])<<8 | uint16(data[2])
+//
+// Bytes [3:3+l] are the string data.
+//
+// If tag data follows then bytes 3+l and 3+l+1 are the tag length,
+// with the data following.
+//
+// If the import path follows, then 4 bytes at the end of
+// the data form a nameOff. The import path is only set for concrete
+// methods that are defined in a different package than their type.
+//
+// If a name starts with "*", then the exported bit represents
+// whether the pointed to type is exported.
+type name struct {
+	bytes *byte
+}
+
+func (n name) data(off int, whySafe string) *byte {
+	return (*byte)(add(unsafe.Pointer(n.bytes), uintptr(off), whySafe))
+}
+
+func (n name) isExported() bool {
+	return (*n.bytes)&(1<<0) != 0
+}
+
+func (n name) nameLen() int {
+	return int(uint16(*n.data(1, "name len field"))<<8 | uint16(*n.data(2, "name len field")))
+}
+
+func (n name) tagLen() int {
+	if *n.data(0, "name flag field")&(1<<1) == 0 {
+		return 0
+	}
+	off := 3 + n.nameLen()
+	return int(uint16(*n.data(off, "name taglen field"))<<8 | uint16(*n.data(off+1, "name taglen field")))
+}
+
+func (n name) name() (s string) {
+	if n.bytes == nil {
+		return
+	}
+	b := (*[4]byte)(unsafe.Pointer(n.bytes))
+
+	hdr := (*stringHeader)(unsafe.Pointer(&s))
+	hdr.Data = unsafe.Pointer(&b[3])
+	hdr.Len = int(b[1])<<8 | int(b[2])
+	return s
+}
+
+func (n name) tag() (s string) {
+	tl := n.tagLen()
+	if tl == 0 {
+		return ""
+	}
+	nl := n.nameLen()
+	hdr := (*stringHeader)(unsafe.Pointer(&s))
+	hdr.Data = unsafe.Pointer(n.data(3+nl+2, "non-empty string"))
+	hdr.Len = tl
+	return s
+}
+
+func (n name) pkgPath() string {
+	if n.bytes == nil || *n.data(0, "name flag field")&(1<<2) == 0 {
+		return ""
+	}
+	off := 3 + n.nameLen()
+	if tl := n.tagLen(); tl > 0 {
+		off += 2 + tl
+	}
+	var nameOff int32
+	// Note that this field may not be aligned in memory,
+	// so we cannot use a direct int32 assignment here.
+	copy((*[4]byte)(unsafe.Pointer(&nameOff))[:], (*[4]byte)(unsafe.Pointer(n.data(off, "name offset field")))[:])
+	pkgPathName := name{(*byte)(resolveTypeOff(unsafe.Pointer(n.bytes), nameOff))}
+	return pkgPathName.name()
+}
+
+/*
+ * The compiler knows the exact layout of all the data structures above.
+ * The compiler does not know about the data structures and methods below.
+ */
+
+const (
+	kindDirectIface = 1 << 5
+	kindGCProg      = 1 << 6 // Type.gc points to GC program
+	kindNoPointers  = 1 << 7
+	kindMask        = (1 << 5) - 1
+)
+
+func (t *uncommonType) methods() []method {
+	if t.mcount == 0 {
+		return nil
+	}
+	return (*[1 << 16]method)(add(unsafe.Pointer(t), uintptr(t.moff), "t.mcount > 0"))[:t.mcount:t.mcount]
+}
+
+func (t *uncommonType) exportedMethods() []method {
+	if t.xcount == 0 {
+		return nil
+	}
+	return (*[1 << 16]method)(add(unsafe.Pointer(t), uintptr(t.moff), "t.xcount > 0"))[:t.xcount:t.xcount]
+}
+
+// resolveNameOff resolves a name offset from a base pointer.
+// The (*rtype).nameOff method is a convenience wrapper for this function.
+// Implemented in the runtime package.
+func resolveNameOff(ptrInModule unsafe.Pointer, off int32) unsafe.Pointer
+
+// resolveTypeOff resolves an *rtype offset from a base type.
+// The (*rtype).typeOff method is a convenience wrapper for this function.
+// Implemented in the runtime package.
+func resolveTypeOff(rtype unsafe.Pointer, off int32) unsafe.Pointer
+
+type nameOff int32 // offset to a name
+type typeOff int32 // offset to an *rtype
+type textOff int32 // offset from top of text section
+
+func (t *rtype) nameOff(off nameOff) name {
+	return name{(*byte)(resolveNameOff(unsafe.Pointer(t), int32(off)))}
+}
+
+func (t *rtype) typeOff(off typeOff) *rtype {
+	return (*rtype)(resolveTypeOff(unsafe.Pointer(t), int32(off)))
+}
+
+func (t *rtype) uncommon() *uncommonType {
+	if t.tflag&tflagUncommon == 0 {
+		return nil
+	}
+	switch t.Kind() {
+	case Struct:
+		return &(*structTypeUncommon)(unsafe.Pointer(t)).u
+	case Ptr:
+		type u struct {
+			ptrType
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	case Func:
+		type u struct {
+			funcType
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	case Slice:
+		type u struct {
+			sliceType
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	case Array:
+		type u struct {
+			arrayType
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	case Chan:
+		type u struct {
+			chanType
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	case Map:
+		type u struct {
+			mapType
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	case Interface:
+		type u struct {
+			interfaceType
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	default:
+		type u struct {
+			rtype
+			u uncommonType
+		}
+		return &(*u)(unsafe.Pointer(t)).u
+	}
+}
+
+func (t *rtype) String() string {
+	s := t.nameOff(t.str).name()
+	if t.tflag&tflagExtraStar != 0 {
+		return s[1:]
+	}
+	return s
+}
+
+func (t *rtype) Kind() Kind { return Kind(t.kind & kindMask) }
+
+func (t *rtype) common() *rtype { return t }
+
+func (t *rtype) exportedMethods() []method {
+	ut := t.uncommon()
+	if ut == nil {
+		return nil
+	}
+	return ut.exportedMethods()
+}
+
+func (t *rtype) NumMethod() int {
+	if t.Kind() == Interface {
+		tt := (*interfaceType)(unsafe.Pointer(t))
+		return tt.NumMethod()
+	}
+	return len(t.exportedMethods())
+}
+
+func (t *rtype) PkgPath() string {
+	if t.tflag&tflagNamed == 0 {
+		return ""
+	}
+	ut := t.uncommon()
+	if ut == nil {
+		return ""
+	}
+	return t.nameOff(ut.pkgPath).name()
+}
+
+func (t *rtype) Name() string {
+	if t.tflag&tflagNamed == 0 {
+		return ""
+	}
+	s := t.String()
+	i := len(s) - 1
+	for i >= 0 {
+		if s[i] == '.' {
+			break
+		}
+		i--
+	}
+	return s[i+1:]
+}
+
+func (t *rtype) chanDir() chanDir {
+	if t.Kind() != Chan {
+		panic("reflect: chanDir of non-chan type")
+	}
+	tt := (*chanType)(unsafe.Pointer(t))
+	return chanDir(tt.dir)
+}
+
+func (t *rtype) Elem() Type {
+	switch t.Kind() {
+	case Array:
+		tt := (*arrayType)(unsafe.Pointer(t))
+		return toType(tt.elem)
+	case Chan:
+		tt := (*chanType)(unsafe.Pointer(t))
+		return toType(tt.elem)
+	case Map:
+		tt := (*mapType)(unsafe.Pointer(t))
+		return toType(tt.elem)
+	case Ptr:
+		tt := (*ptrType)(unsafe.Pointer(t))
+		return toType(tt.elem)
+	case Slice:
+		tt := (*sliceType)(unsafe.Pointer(t))
+		return toType(tt.elem)
+	}
+	panic("reflect: Elem of invalid type")
+}
+
+func (t *rtype) In(i int) Type {
+	if t.Kind() != Func {
+		panic("reflect: In of non-func type")
+	}
+	tt := (*funcType)(unsafe.Pointer(t))
+	return toType(tt.in()[i])
+}
+
+func (t *rtype) Key() Type {
+	if t.Kind() != Map {
+		panic("reflect: Key of non-map type")
+	}
+	tt := (*mapType)(unsafe.Pointer(t))
+	return toType(tt.key)
+}
+
+func (t *rtype) Len() int {
+	if t.Kind() != Array {
+		panic("reflect: Len of non-array type")
+	}
+	tt := (*arrayType)(unsafe.Pointer(t))
+	return int(tt.len)
+}
+
+func (t *rtype) NumField() int {
+	if t.Kind() != Struct {
+		panic("reflect: NumField of non-struct type")
+	}
+	tt := (*structType)(unsafe.Pointer(t))
+	return len(tt.fields)
+}
+
+func (t *rtype) NumIn() int {
+	if t.Kind() != Func {
+		panic("reflect: NumIn of non-func type")
+	}
+	tt := (*funcType)(unsafe.Pointer(t))
+	return int(tt.inCount)
+}
+
+func (t *rtype) NumOut() int {
+	if t.Kind() != Func {
+		panic("reflect: NumOut of non-func type")
+	}
+	tt := (*funcType)(unsafe.Pointer(t))
+	return len(tt.out())
+}
+
+func (t *rtype) Out(i int) Type {
+	if t.Kind() != Func {
+		panic("reflect: Out of non-func type")
+	}
+	tt := (*funcType)(unsafe.Pointer(t))
+	return toType(tt.out()[i])
+}
+
+func (t *funcType) in() []*rtype {
+	uadd := unsafe.Sizeof(*t)
+	if t.tflag&tflagUncommon != 0 {
+		uadd += unsafe.Sizeof(uncommonType{})
+	}
+	if t.inCount == 0 {
+		return nil
+	}
+	return (*[1 << 20]*rtype)(add(unsafe.Pointer(t), uadd, "t.inCount > 0"))[:t.inCount]
+}
+
+func (t *funcType) out() []*rtype {
+	uadd := unsafe.Sizeof(*t)
+	if t.tflag&tflagUncommon != 0 {
+		uadd += unsafe.Sizeof(uncommonType{})
+	}
+	outCount := t.outCount & (1<<15 - 1)
+	if outCount == 0 {
+		return nil
+	}
+	return (*[1 << 20]*rtype)(add(unsafe.Pointer(t), uadd, "outCount > 0"))[t.inCount : t.inCount+outCount]
+}
+
+// add returns p+x.
+//
+// The whySafe string is ignored, so that the function still inlines
+// as efficiently as p+x, but all call sites should use the string to
+// record why the addition is safe, which is to say why the addition
+// does not cause x to advance to the very end of p's allocation
+// and therefore point incorrectly at the next block in memory.
+func add(p unsafe.Pointer, x uintptr, whySafe string) unsafe.Pointer {
+	return unsafe.Pointer(uintptr(p) + x)
+}
+
+// NumMethod returns the number of interface methods in the type's method set.
+func (t *interfaceType) NumMethod() int { return len(t.methods) }
+
+// TypeOf returns the reflection Type that represents the dynamic type of i.
+// If i is a nil interface value, TypeOf returns nil.
+func TypeOf(i interface{}) Type {
+	eface := *(*emptyInterface)(unsafe.Pointer(&i))
+	return toType(eface.typ)
+}
+
+func (t *rtype) Implements(u Type) bool {
+	if u == nil {
+		panic("reflect: nil type passed to Type.Implements")
+	}
+	if u.Kind() != Interface {
+		panic("reflect: non-interface type passed to Type.Implements")
+	}
+	return implements(u.(*rtype), t)
+}
+
+func (t *rtype) AssignableTo(u Type) bool {
+	if u == nil {
+		panic("reflect: nil type passed to Type.AssignableTo")
+	}
+	uu := u.(*rtype)
+	return directlyAssignable(uu, t) || implements(uu, t)
+}
+
+// implements reports whether the type V implements the interface type T.
+func implements(T, V *rtype) bool {
+	if T.Kind() != Interface {
+		return false
+	}
+	t := (*interfaceType)(unsafe.Pointer(T))
+	if len(t.methods) == 0 {
+		return true
+	}
+
+	// The same algorithm applies in both cases, but the
+	// method tables for an interface type and a concrete type
+	// are different, so the code is duplicated.
+	// In both cases the algorithm is a linear scan over the two
+	// lists - T's methods and V's methods - simultaneously.
+	// Since method tables are stored in a unique sorted order
+	// (alphabetical, with no duplicate method names), the scan
+	// through V's methods must hit a match for each of T's
+	// methods along the way, or else V does not implement T.
+	// This lets us run the scan in overall linear time instead of
+	// the quadratic time  a naive search would require.
+	// See also ../runtime/iface.go.
+	if V.Kind() == Interface {
+		v := (*interfaceType)(unsafe.Pointer(V))
+		i := 0
+		for j := 0; j < len(v.methods); j++ {
+			tm := &t.methods[i]
+			tmName := t.nameOff(tm.name)
+			vm := &v.methods[j]
+			vmName := V.nameOff(vm.name)
+			if vmName.name() == tmName.name() && V.typeOff(vm.typ) == t.typeOff(tm.typ) {
+				if !tmName.isExported() {
+					tmPkgPath := tmName.pkgPath()
+					if tmPkgPath == "" {
+						tmPkgPath = t.pkgPath.name()
+					}
+					vmPkgPath := vmName.pkgPath()
+					if vmPkgPath == "" {
+						vmPkgPath = v.pkgPath.name()
+					}
+					if tmPkgPath != vmPkgPath {
+						continue
+					}
+				}
+				if i++; i >= len(t.methods) {
+					return true
+				}
+			}
+		}
+		return false
+	}
+
+	v := V.uncommon()
+	if v == nil {
+		return false
+	}
+	i := 0
+	vmethods := v.methods()
+	for j := 0; j < int(v.mcount); j++ {
+		tm := &t.methods[i]
+		tmName := t.nameOff(tm.name)
+		vm := vmethods[j]
+		vmName := V.nameOff(vm.name)
+		if vmName.name() == tmName.name() && V.typeOff(vm.mtyp) == t.typeOff(tm.typ) {
+			if !tmName.isExported() {
+				tmPkgPath := tmName.pkgPath()
+				if tmPkgPath == "" {
+					tmPkgPath = t.pkgPath.name()
+				}
+				vmPkgPath := vmName.pkgPath()
+				if vmPkgPath == "" {
+					vmPkgPath = V.nameOff(v.pkgPath).name()
+				}
+				if tmPkgPath != vmPkgPath {
+					continue
+				}
+			}
+			if i++; i >= len(t.methods) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// directlyAssignable reports whether a value x of type V can be directly
+// assigned (using memmove) to a value of type T.
+// https://golang.org/doc/go_spec.html#Assignability
+// Ignoring the interface rules (implemented elsewhere)
+// and the ideal constant rules (no ideal constants at run time).
+func directlyAssignable(T, V *rtype) bool {
+	// x's type V is identical to T?
+	if T == V {
+		return true
+	}
+
+	// Otherwise at least one of T and V must not be defined
+	// and they must have the same kind.
+	if T.Name() != "" && V.Name() != "" || T.Kind() != V.Kind() {
+		return false
+	}
+
+	// x's type T and V must  have identical underlying types.
+	return haveIdenticalUnderlyingType(T, V, true)
+}
+
+func haveIdenticalType(T, V Type, cmpTags bool) bool {
+	if cmpTags {
+		return T == V
+	}
+
+	if T.Name() != V.Name() || T.Kind() != V.Kind() {
+		return false
+	}
+
+	return haveIdenticalUnderlyingType(T.common(), V.common(), false)
+}
+
+func haveIdenticalUnderlyingType(T, V *rtype, cmpTags bool) bool {
+	if T == V {
+		return true
+	}
+
+	kind := T.Kind()
+	if kind != V.Kind() {
+		return false
+	}
+
+	// Non-composite types of equal kind have same underlying type
+	// (the predefined instance of the type).
+	if Bool <= kind && kind <= Complex128 || kind == String || kind == UnsafePointer {
+		return true
+	}
+
+	// Composite types.
+	switch kind {
+	case Array:
+		return T.Len() == V.Len() && haveIdenticalType(T.Elem(), V.Elem(), cmpTags)
+
+	case Chan:
+		// Special case:
+		// x is a bidirectional channel value, T is a channel type,
+		// and x's type V and T have identical element types.
+		if V.chanDir() == bothDir && haveIdenticalType(T.Elem(), V.Elem(), cmpTags) {
+			return true
+		}
+
+		// Otherwise continue test for identical underlying type.
+		return V.chanDir() == T.chanDir() && haveIdenticalType(T.Elem(), V.Elem(), cmpTags)
+
+	case Func:
+		t := (*funcType)(unsafe.Pointer(T))
+		v := (*funcType)(unsafe.Pointer(V))
+		if t.outCount != v.outCount || t.inCount != v.inCount {
+			return false
+		}
+		for i := 0; i < t.NumIn(); i++ {
+			if !haveIdenticalType(t.In(i), v.In(i), cmpTags) {
+				return false
+			}
+		}
+		for i := 0; i < t.NumOut(); i++ {
+			if !haveIdenticalType(t.Out(i), v.Out(i), cmpTags) {
+				return false
+			}
+		}
+		return true
+
+	case Interface:
+		t := (*interfaceType)(unsafe.Pointer(T))
+		v := (*interfaceType)(unsafe.Pointer(V))
+		if len(t.methods) == 0 && len(v.methods) == 0 {
+			return true
+		}
+		// Might have the same methods but still
+		// need a run time conversion.
+		return false
+
+	case Map:
+		return haveIdenticalType(T.Key(), V.Key(), cmpTags) && haveIdenticalType(T.Elem(), V.Elem(), cmpTags)
+
+	case Ptr, Slice:
+		return haveIdenticalType(T.Elem(), V.Elem(), cmpTags)
+
+	case Struct:
+		t := (*structType)(unsafe.Pointer(T))
+		v := (*structType)(unsafe.Pointer(V))
+		if len(t.fields) != len(v.fields) {
+			return false
+		}
+		if t.pkgPath.name() != v.pkgPath.name() {
+			return false
+		}
+		for i := range t.fields {
+			tf := &t.fields[i]
+			vf := &v.fields[i]
+			if tf.name.name() != vf.name.name() {
+				return false
+			}
+			if !haveIdenticalType(tf.typ, vf.typ, cmpTags) {
+				return false
+			}
+			if cmpTags && tf.name.tag() != vf.name.tag() {
+				return false
+			}
+			if tf.offsetEmbed != vf.offsetEmbed {
+				return false
+			}
+		}
+		return true
+	}
+
+	return false
+}
+
+type structTypeUncommon struct {
+	structType
+	u uncommonType
+}
+
+// toType converts from a *rtype to a Type that can be returned
+// to the client of package reflect. In gc, the only concern is that
+// a nil *rtype must be replaced by a nil Type, but in gccgo this
+// function takes care of ensuring that multiple *rtype for the same
+// type are coalesced into a single Type.
+func toType(t *rtype) Type {
+	if t == nil {
+		return nil
+	}
+	return t
+}
+
+// ifaceIndir reports whether t is stored indirectly in an interface value.
+func ifaceIndir(t *rtype) bool {
+	return t.kind&kindDirectIface == 0
+}

src/internal/reflectlite/value.go

@@ -0,0 +1,448 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflectlite
+
+import (
+	"runtime"
+	"unsafe"
+)
+
+// Value is the reflection interface to a Go value.
+//
+// Not all methods apply to all kinds of values. Restrictions,
+// if any, are noted in the documentation for each method.
+// Use the Kind method to find out the kind of value before
+// calling kind-specific methods. Calling a method
+// inappropriate to the kind of type causes a run time panic.
+//
+// The zero Value represents no value.
+// Its IsValid method returns false, its Kind method returns Invalid,
+// its String method returns "<invalid Value>", and all other methods panic.
+// Most functions and methods never return an invalid value.
+// If one does, its documentation states the conditions explicitly.
+//
+// A Value can be used concurrently by multiple goroutines provided that
+// the underlying Go value can be used concurrently for the equivalent
+// direct operations.
+//
+// To compare two Values, compare the results of the Interface method.
+// Using == on two Values does not compare the underlying values
+// they represent.
+type Value struct {
+	// typ holds the type of the value represented by a Value.
+	typ *rtype
+
+	// Pointer-valued data or, if flagIndir is set, pointer to data.
+	// Valid when either flagIndir is set or typ.pointers() is true.
+	ptr unsafe.Pointer
+
+	// flag holds metadata about the value.
+	// The lowest bits are flag bits:
+	//	- flagStickyRO: obtained via unexported not embedded field, so read-only
+	//	- flagEmbedRO: obtained via unexported embedded field, so read-only
+	//	- flagIndir: val holds a pointer to the data
+	//	- flagAddr: v.CanAddr is true (implies flagIndir)
+	// Value cannot represent method values.
+	// The next five bits give the Kind of the value.
+	// This repeats typ.Kind() except for method values.
+	// The remaining 23+ bits give a method number for method values.
+	// If flag.kind() != Func, code can assume that flagMethod is unset.
+	// If ifaceIndir(typ), code can assume that flagIndir is set.
+	flag
+
+	// A method value represents a curried method invocation
+	// like r.Read for some receiver r. The typ+val+flag bits describe
+	// the receiver r, but the flag's Kind bits say Func (methods are
+	// functions), and the top bits of the flag give the method number
+	// in r's type's method table.
+}
+
+type flag uintptr
+
+const (
+	flagKindWidth        = 5 // there are 27 kinds
+	flagKindMask    flag = 1<<flagKindWidth - 1
+	flagStickyRO    flag = 1 << 5
+	flagEmbedRO     flag = 1 << 6
+	flagIndir       flag = 1 << 7
+	flagAddr        flag = 1 << 8
+	flagMethod      flag = 1 << 9
+	flagMethodShift      = 10
+	flagRO          flag = flagStickyRO | flagEmbedRO
+)
+
+func (f flag) kind() Kind {
+	return Kind(f & flagKindMask)
+}
+
+func (f flag) ro() flag {
+	if f&flagRO != 0 {
+		return flagStickyRO
+	}
+	return 0
+}
+
+// packEface converts v to the empty interface.
+func packEface(v Value) interface{} {
+	t := v.typ
+	var i interface{}
+	e := (*emptyInterface)(unsafe.Pointer(&i))
+	// First, fill in the data portion of the interface.
+	switch {
+	case ifaceIndir(t):
+		if v.flag&flagIndir == 0 {
+			panic("bad indir")
+		}
+		// Value is indirect, and so is the interface we're making.
+		ptr := v.ptr
+		if v.flag&flagAddr != 0 {
+			// TODO: pass safe boolean from valueInterface so
+			// we don't need to copy if safe==true?
+			c := unsafe_New(t)
+			typedmemmove(t, c, ptr)
+			ptr = c
+		}
+		e.word = ptr
+	case v.flag&flagIndir != 0:
+		// Value is indirect, but interface is direct. We need
+		// to load the data at v.ptr into the interface data word.
+		e.word = *(*unsafe.Pointer)(v.ptr)
+	default:
+		// Value is direct, and so is the interface.
+		e.word = v.ptr
+	}
+	// Now, fill in the type portion. We're very careful here not
+	// to have any operation between the e.word and e.typ assignments
+	// that would let the garbage collector observe the partially-built
+	// interface value.
+	e.typ = t
+	return i
+}
+
+// unpackEface converts the empty interface i to a Value.
+func unpackEface(i interface{}) Value {
+	e := (*emptyInterface)(unsafe.Pointer(&i))
+	// NOTE: don't read e.word until we know whether it is really a pointer or not.
+	t := e.typ
+	if t == nil {
+		return Value{}
+	}
+	f := flag(t.Kind())
+	if ifaceIndir(t) {
+		f |= flagIndir
+	}
+	return Value{t, e.word, f}
+}
+
+// A ValueError occurs when a Value method is invoked on
+// a Value that does not support it. Such cases are documented
+// in the description of each method.
+type ValueError struct {
+	Method string
+	Kind   Kind
+}
+
+func (e *ValueError) Error() string {
+	return "reflect: call of " + e.Method + " on zero Value"
+}
+
+// methodName returns the name of the calling method,
+// assumed to be two stack frames above.
+func methodName() string {
+	pc, _, _, _ := runtime.Caller(2)
+	f := runtime.FuncForPC(pc)
+	if f == nil {
+		return "unknown method"
+	}
+	return f.Name()
+}
+
+// emptyInterface is the header for an interface{} value.
+type emptyInterface struct {
+	typ  *rtype
+	word unsafe.Pointer
+}
+
+// nonEmptyInterface is the header for an interface value with methods.
+type nonEmptyInterface struct {
+	// see ../runtime/iface.go:/Itab
+	itab *struct {
+		ityp *rtype // static interface type
+		typ  *rtype // dynamic concrete type
+		hash uint32 // copy of typ.hash
+		_    [4]byte
+		fun  [100000]unsafe.Pointer // method table
+	}
+	word unsafe.Pointer
+}
+
+// mustBeExported panics if f records that the value was obtained using
+// an unexported field.
+func (f flag) mustBeExported() {
+	if f == 0 {
+		panic(&ValueError{methodName(), 0})
+	}
+	if f&flagRO != 0 {
+		panic("reflect: " + methodName() + " using value obtained using unexported field")
+	}
+}
+
+// mustBeAssignable panics if f records that the value is not assignable,
+// which is to say that either it was obtained using an unexported field
+// or it is not addressable.
+func (f flag) mustBeAssignable() {
+	if f == 0 {
+		panic(&ValueError{methodName(), Invalid})
+	}
+	// Assignable if addressable and not read-only.
+	if f&flagRO != 0 {
+		panic("reflect: " + methodName() + " using value obtained using unexported field")
+	}
+	if f&flagAddr == 0 {
+		panic("reflect: " + methodName() + " using unaddressable value")
+	}
+}
+
+// CanSet reports whether the value of v can be changed.
+// A Value can be changed only if it is addressable and was not
+// obtained by the use of unexported struct fields.
+// If CanSet returns false, calling Set or any type-specific
+// setter (e.g., SetBool, SetInt) will panic.
+func (v Value) CanSet() bool {
+	return v.flag&(flagAddr|flagRO) == flagAddr
+}
+
+// Elem returns the value that the interface v contains
+// or that the pointer v points to.
+// It panics if v's Kind is not Interface or Ptr.
+// It returns the zero Value if v is nil.
+func (v Value) Elem() Value {
+	k := v.kind()
+	switch k {
+	case Interface:
+		var eface interface{}
+		if v.typ.NumMethod() == 0 {
+			eface = *(*interface{})(v.ptr)
+		} else {
+			eface = (interface{})(*(*interface {
+				M()
+			})(v.ptr))
+		}
+		x := unpackEface(eface)
+		if x.flag != 0 {
+			x.flag |= v.flag.ro()
+		}
+		return x
+	case Ptr:
+		ptr := v.ptr
+		if v.flag&flagIndir != 0 {
+			ptr = *(*unsafe.Pointer)(ptr)
+		}
+		// The returned value's address is v's value.
+		if ptr == nil {
+			return Value{}
+		}
+		tt := (*ptrType)(unsafe.Pointer(v.typ))
+		typ := tt.elem
+		fl := v.flag&flagRO | flagIndir | flagAddr
+		fl |= flag(typ.Kind())
+		return Value{typ, ptr, fl}
+	}
+	panic(&ValueError{"reflectlite.Value.Elem", v.kind()})
+}
+
+func valueInterface(v Value) interface{} {
+	if v.flag == 0 {
+		panic(&ValueError{"reflectlite.Value.Interface", 0})
+	}
+
+	if v.kind() == Interface {
+		// Special case: return the element inside the interface.
+		// Empty interface has one layout, all interfaces with
+		// methods have a second layout.
+		if v.numMethod() == 0 {
+			return *(*interface{})(v.ptr)
+		}
+		return *(*interface {
+			M()
+		})(v.ptr)
+	}
+
+	// TODO: pass safe to packEface so we don't need to copy if safe==true?
+	return packEface(v)
+}
+
+// IsNil reports whether its argument v is nil. The argument must be
+// a chan, func, interface, map, pointer, or slice value; if it is
+// not, IsNil panics. Note that IsNil is not always equivalent to a
+// regular comparison with nil in Go. For example, if v was created
+// by calling ValueOf with an uninitialized interface variable i,
+// i==nil will be true but v.IsNil will panic as v will be the zero
+// Value.
+func (v Value) IsNil() bool {
+	k := v.kind()
+	switch k {
+	case Chan, Func, Map, Ptr, UnsafePointer:
+		// if v.flag&flagMethod != 0 {
+		// 	return false
+		// }
+		ptr := v.ptr
+		if v.flag&flagIndir != 0 {
+			ptr = *(*unsafe.Pointer)(ptr)
+		}
+		return ptr == nil
+	case Interface, Slice:
+		// Both interface and slice are nil if first word is 0.
+		// Both are always bigger than a word; assume flagIndir.
+		return *(*unsafe.Pointer)(v.ptr) == nil
+	}
+	panic(&ValueError{"reflectlite.Value.IsNil", v.kind()})
+}
+
+// IsValid reports whether v represents a value.
+// It returns false if v is the zero Value.
+// If IsValid returns false, all other methods except String panic.
+// Most functions and methods never return an invalid value.
+// If one does, its documentation states the conditions explicitly.
+func (v Value) IsValid() bool {
+	return v.flag != 0
+}
+
+// Kind returns v's Kind.
+// If v is the zero Value (IsValid returns false), Kind returns Invalid.
+func (v Value) Kind() Kind {
+	return v.kind()
+}
+
+// NumMethod returns the number of exported methods in the value's method set.
+func (v Value) numMethod() int {
+	if v.typ == nil {
+		panic(&ValueError{"reflectlite.Value.NumMethod", Invalid})
+	}
+	return v.typ.NumMethod()
+}
+
+// Set assigns x to the value v.
+// It panics if CanSet returns false.
+// As in Go, x's value must be assignable to v's type.
+func (v Value) Set(x Value) {
+	v.mustBeAssignable()
+	x.mustBeExported() // do not let unexported x leak
+	var target unsafe.Pointer
+	if v.kind() == Interface {
+		target = v.ptr
+	}
+	x = x.assignTo("reflectlite.Set", v.typ, target)
+	if x.flag&flagIndir != 0 {
+		typedmemmove(v.typ, v.ptr, x.ptr)
+	} else {
+		*(*unsafe.Pointer)(v.ptr) = x.ptr
+	}
+}
+
+// Type returns v's type.
+func (v Value) Type() Type {
+	f := v.flag
+	if f == 0 {
+		panic(&ValueError{"reflectlite.Value.Type", Invalid})
+	}
+	// Method values not supported.
+	return v.typ
+}
+
+// stringHeader is a safe version of StringHeader used within this package.
+type stringHeader struct {
+	Data unsafe.Pointer
+	Len  int
+}
+
+// sliceHeader is a safe version of SliceHeader used within this package.
+type sliceHeader struct {
+	Data unsafe.Pointer
+	Len  int
+	Cap  int
+}
+
+/*
+ * constructors
+ */
+
+// implemented in package runtime
+func unsafe_New(*rtype) unsafe.Pointer
+
+// ValueOf returns a new Value initialized to the concrete value
+// stored in the interface i. ValueOf(nil) returns the zero Value.
+func ValueOf(i interface{}) Value {
+	if i == nil {
+		return Value{}
+	}
+
+	// TODO: Maybe allow contents of a Value to live on the stack.
+	// For now we make the contents always escape to the heap. It
+	// makes life easier in a few places (see chanrecv/mapassign
+	// comment below).
+	escapes(i)
+
+	return unpackEface(i)
+}
+
+// assignTo returns a value v that can be assigned directly to typ.
+// It panics if v is not assignable to typ.
+// For a conversion to an interface type, target is a suggested scratch space to use.
+func (v Value) assignTo(context string, dst *rtype, target unsafe.Pointer) Value {
+	// if v.flag&flagMethod != 0 {
+	// 	v = makeMethodValue(context, v)
+	// }
+
+	switch {
+	case directlyAssignable(dst, v.typ):
+		// Overwrite type so that they match.
+		// Same memory layout, so no harm done.
+		fl := v.flag&(flagAddr|flagIndir) | v.flag.ro()
+		fl |= flag(dst.Kind())
+		return Value{dst, v.ptr, fl}
+
+	case implements(dst, v.typ):
+		if target == nil {
+			target = unsafe_New(dst)
+		}
+		if v.Kind() == Interface && v.IsNil() {
+			// A nil ReadWriter passed to nil Reader is OK,
+			// but using ifaceE2I below will panic.
+			// Avoid the panic by returning a nil dst (e.g., Reader) explicitly.
+			return Value{dst, nil, flag(Interface)}
+		}
+		x := valueInterface(v)
+		if dst.NumMethod() == 0 {
+			*(*interface{})(target) = x
+		} else {
+			ifaceE2I(dst, x, target)
+		}
+		return Value{dst, target, flagIndir | flag(Interface)}
+	}
+
+	// Failed.
+	panic(context + ": value of type " + v.typ.String() + " is not assignable to type " + dst.String())
+}
+
+func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer)
+
+// typedmemmove copies a value of type t to dst from src.
+//go:noescape
+func typedmemmove(t *rtype, dst, src unsafe.Pointer)
+
+// Dummy annotation marking that the value x escapes,
+// for use in cases where the reflect code is so clever that
+// the compiler cannot follow.
+func escapes(x interface{}) {
+	if dummy.b {
+		dummy.x = x
+	}
+}
+
+var dummy struct {
+	b bool
+	x interface{}
+}

src/runtime/iface.go

@@ -492,6 +492,11 @@ func reflect_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
 	*dst = assertE2I(inter, e)
 }
 
+//go:linkname reflectlite_ifaceE2I internal/reflectlite.ifaceE2I
+func reflectlite_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
+	*dst = assertE2I(inter, e)
+}
+
 func iterate_itabs(fn func(*itab)) {
 	// Note: only runs during stop the world or with itabLock held,
 	// so no other locks/atomics needed.

src/runtime/malloc.go

@@ -1073,6 +1073,11 @@ func reflect_unsafe_New(typ *_type) unsafe.Pointer {
 	return mallocgc(typ.size, typ, true)
 }
 
+//go:linkname reflectlite_unsafe_New internal/reflectlite.unsafe_New
+func reflectlite_unsafe_New(typ *_type) unsafe.Pointer {
+	return mallocgc(typ.size, typ, true)
+}
+
 // newarray allocates an array of n elements of type typ.
 func newarray(typ *_type, n int) unsafe.Pointer {
 	if n == 1 {

src/runtime/mbarrier.go

@@ -186,6 +186,11 @@ func reflect_typedmemmove(typ *_type, dst, src unsafe.Pointer) {
 	typedmemmove(typ, dst, src)
 }
 
+//go:linkname reflectlite_typedmemmove internal/reflectlite.typedmemmove
+func reflectlite_typedmemmove(typ *_type, dst, src unsafe.Pointer) {
+	reflect_typedmemmove(typ, dst, src)
+}
+
 // typedmemmovepartial is like typedmemmove but assumes that
 // dst and src point off bytes into the value and only copies size bytes.
 //go:linkname reflect_typedmemmovepartial reflect.typedmemmovepartial

src/runtime/runtime1.go

@@ -490,6 +490,18 @@ func reflect_resolveTextOff(rtype unsafe.Pointer, off int32) unsafe.Pointer {
 
 }
 
+// reflectlite_resolveNameOff resolves a name offset from a base pointer.
+//go:linkname reflectlite_resolveNameOff internal/reflectlite.resolveNameOff
+func reflectlite_resolveNameOff(ptrInModule unsafe.Pointer, off int32) unsafe.Pointer {
+	return unsafe.Pointer(resolveNameOff(ptrInModule, nameOff(off)).bytes)
+}
+
+// reflectlite_resolveTypeOff resolves an *rtype offset from a base type.
+//go:linkname reflectlite_resolveTypeOff internal/reflectlite.resolveTypeOff
+func reflectlite_resolveTypeOff(rtype unsafe.Pointer, off int32) unsafe.Pointer {
+	return unsafe.Pointer((*_type)(rtype).typeOff(typeOff(off)))
+}
+
 // reflect_addReflectOff adds a pointer to the reflection offset lookup map.
 //go:linkname reflect_addReflectOff reflect.addReflectOff
 func reflect_addReflectOff(ptr unsafe.Pointer) int32 {