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reflect: allow conversion from slice to array ptr

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Note that this removes an invariant:

v.Type().ConvertibleTo(t) might return true,
yet v.Convert(t) might panic nevertheless.

This is a fairly unavoidable consequence of the decision
to add the first-ever conversion that can panic.

ConvertibleTo describes a relationship between types,
but whether the conversion panics now depends on the value,
not just the type.

If this turns out to be a problem, we can add v.ConvertibleTo(t),
or something similar, to allow callers to avoid the panic.

This is the last of the changes needed to complete the implementation.

Fixes #395

Change-Id: I79b7e4dd87a67a47723e00a65d0b1ac6090371b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/301652
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Josh Bleecher Snyder 2021-03-14 14:31:50 -07:00
parent c18744377a
commit 760d3b2a16
3 changed files with 63 additions and 1 deletions
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44
src/reflect/all_test.go
View file

@ -3822,6 +3822,10 @@ type MyStruct2 struct {
}
type MyString string
type MyBytes []byte
type MyBytesArrayPtr0 *[0]byte
type MyBytesArrayPtr *[4]byte
type MyBytesArray0 [0]byte
type MyBytesArray [4]byte
type MyRunes []int32
type MyFunc func()
type MyByte byte
@ -4128,6 +4132,30 @@ var convertTests = []struct {
{V(MyString("runes♝")), V(MyRunes("runes♝"))},
{V(MyRunes("runes♕")), V(MyString("runes♕"))},
// slice to array pointer
{V([]byte(nil)), V((*[0]byte)(nil))},
{V([]byte{}), V(new([0]byte))},
{V([]byte{7}), V(&[1]byte{7})},
{V(MyBytes([]byte(nil))), V((*[0]byte)(nil))},
{V(MyBytes([]byte{})), V(new([0]byte))},
{V(MyBytes([]byte{9})), V(&[1]byte{9})},
{V([]byte(nil)), V(MyBytesArrayPtr0(nil))},
{V([]byte{}), V(MyBytesArrayPtr0(new([0]byte)))},
{V([]byte{1, 2, 3, 4}), V(MyBytesArrayPtr(&[4]byte{1, 2, 3, 4}))},
{V(MyBytes([]byte{})), V(MyBytesArrayPtr0(new([0]byte)))},
{V(MyBytes([]byte{5, 6, 7, 8})), V(MyBytesArrayPtr(&[4]byte{5, 6, 7, 8}))},
{V([]byte(nil)), V((*MyBytesArray0)(nil))},
{V([]byte{}), V((*MyBytesArray0)(new([0]byte)))},
{V([]byte{1, 2, 3, 4}), V(&MyBytesArray{1, 2, 3, 4})},
{V(MyBytes([]byte(nil))), V((*MyBytesArray0)(nil))},
{V(MyBytes([]byte{})), V((*MyBytesArray0)(new([0]byte)))},
{V(MyBytes([]byte{5, 6, 7, 8})), V(&MyBytesArray{5, 6, 7, 8})},
{V(new([0]byte)), V(new(MyBytesArray0))},
{V(new(MyBytesArray0)), V(new([0]byte))},
{V(MyBytesArrayPtr0(nil)), V((*[0]byte)(nil))},
{V((*[0]byte)(nil)), V(MyBytesArrayPtr0(nil))},
// named types and equal underlying types
{V(new(int)), V(new(integer))},
{V(new(integer)), V(new(int))},
@ -4288,6 +4316,9 @@ func TestConvert(t *testing.T) {
if vout2.Type() != tt.out.Type() || !DeepEqual(out2, tt.out.Interface()) {
t.Errorf("ValueOf(%T(%[1]v)).Convert(%s) = %T(%[3]v), want %T(%[4]v)", tt.in.Interface(), t2, out2, tt.out.Interface())
}
if got, want := vout2.Kind(), vout2.Type().Kind(); got != want {
t.Errorf("ValueOf(%T(%[1]v)).Convert(%s) has internal kind %v want %v", tt.in.Interface(), t1, got, want)
}
// vout3 represents a new value of the out type, set to vout2. This makes
// sure the converted value vout2 is really usable as a regular value.
@ -4332,6 +4363,19 @@ func TestConvert(t *testing.T) {
}
}
func TestConvertPanic(t *testing.T) {
s := make([]byte, 4)
p := new([8]byte)
v := ValueOf(s)
pt := TypeOf(p)
if !v.Type().ConvertibleTo(pt) {
t.Errorf("[]byte should be convertible to *[8]byte")
}
shouldPanic("reflect: cannot convert slice with length 4 to array pointer with length 8", func() {
_ = v.Convert(pt)
})
}
var gFloat32 float32
func TestConvertNaNs(t *testing.T) {