diff --git a/doc/go_spec.html b/doc/go_spec.html index fff489c33ac..8ff178e2810 100644 --- a/doc/go_spec.html +++ b/doc/go_spec.html @@ -1,6 +1,6 @@ @@ -798,7 +798,6 @@ If a variable has not yet been assigned a value, its value is the zero value for its type.

-

Types

@@ -1200,7 +1199,7 @@ type (

A pointer type denotes the set of all pointers to variables of a given type, called the base type of the pointer. -The value of an uninitialized pointer is nil. +The value of an uninitialized pointer is nil. 

@@ -1216,9 +1215,9 @@ BaseType    = Type .
 
Function types

 
 

-A function type denotes the set of all functions with the same parameter
-and result types. The value of an uninitialized variable of function type
-is nil.
+A function type denotes the set of all functions with the same parameter and result types.
+The value of an uninitialized variable of function
+type is nil.
 

 
 
@@ -1267,7 +1266,8 @@ An interface type defines a type set.
 A variable of interface type can store a value of any type that is in the type
 set of the interface. Such a type is said to
 implement the interface.
-The value of an uninitialized variable of interface type is nil.
+The value of an uninitialized variable of
+interface type is nil.
 

 
 
@@ -1630,7 +1630,7 @@ implements the interface.
 A map is an unordered group of elements of one type, called the
 element type, indexed by a set of unique keys of another type,
 called the key type.
-The value of an uninitialized map is nil.
+The value of an uninitialized map is nil.
 

 
 
@@ -1693,7 +1693,7 @@ to communicate by
 sending and
 receiving
 values of a specified element type.
-The value of an uninitialized channel is nil.
+The value of an uninitialized channel is nil.
 

 
 
@@ -1772,6 +1772,57 @@ received in the order sent.
 
 
Properties of types and values

 
+
Representation of values

+
+

+Values of predeclared types (see below for the interfaces any
+and error), arrays, and structs are self-contained:
+Each such value contains a complete copy of all its data,
+and variables of such types store the entire value.
+For instance, an array variable provides the storage (the variables)
+for all elements of the array.
+The respective zero values are specific to the
+value's types; they are never nil.
+

+
+

+Non-nil pointer, function, slice, map, and channel values contain references
+to underlying data which may be shared by multiple values:
+

+
+
    
+
  • 
+	A pointer value is a reference to the variable holding
+	the pointer base type value.
+
    • 
+
  • 
+	A function value contains references to the (possibly
+	anonymous) function
+	and enclosed variables.
+
    • 
+
  • 
+	A slice value contains the slice length, capacity, and
+	a reference to its underlying array.
+
    • 
+
  • 
+	A map or channel value is a reference to the implementation-specific
+	data structure of the map or channel.
+
    • 
+

+
+

+An interface value may be self-contained or contain references to underlying data
+depending on the interface's dynamic type.
+The predeclared identifier nil is the zero value for types whose values
+can contain references.
+

+
+

+When multiple values share underlying data, changing one value may change another.
+For instance, changing an element of a slice will change
+that element in the underlying array for all slices that share the array.
+

+
 
Underlying types

 
 

@@ -2899,7 +2950,7 @@ initialization value in the assignment.
 If that value is an untyped constant, it is first implicitly
 converted to its default type;
 if it is an untyped boolean value, it is first implicitly converted to type bool.
-The predeclared value nil cannot be used to initialize a variable
+The predeclared identifier nil cannot be used to initialize a variable
 with no explicit type.
 

 
@@ -6263,6 +6314,26 @@ to the type of the operand to which it is assigned, with the following special c
 
 
 
+

+When a value is assigned to a variable, only the data that is stored in the variable
+is replaced. If the value contains a reference,
+the assignment copies the reference but does not make a copy of the referenced data
+(such as the underlying array of a slice).
+

+
+
+var s1 = []int{1, 2, 3}
+var s2 = s1                    // s2 stores the slice descriptor of s1
+s1 = s1[:1]                    // s1's length is 1 but it still shares its underlying array with s2
+s2[0] = 42                     // setting s2[0] changes s1[0] as well
+fmt.Println(s1, s2)            // prints [42] [42 2 3]
+
+var m1 = make(map[string]int)
+var m2 = m1                    // m2 stores the map descriptor of m1
+m1["foo"] = 42                 // setting m1["foo"] changes m2["foo"] as well
+fmt.Println(m2["foo"])         // prints 42
+

+
 
If statements