diff --git a/doc/go_spec.html b/doc/go_spec.html index de79f7ee4b..7fa02e4192 100644 --- a/doc/go_spec.html +++ b/doc/go_spec.html @@ -1,6 +1,6 @@ @@ -577,7 +577,7 @@ Numeric constants represent values of arbitrary precision and do not overflow.

-Constants may be typed or untyped. +Constants may be typed or untyped. Literal constants, true, false, iota, and certain constant expressions containing only untyped constant operands are untyped. @@ -597,6 +597,17 @@ can be given the types float32, float64, or uint not int32 or string.

+

+An untyped constant has a default type which is the type to which the +constant is implicitly converted in contexts where a typed value is required, +for instance, in a short variable declaration +such as i := 0 where there is no explicit type. +The default type of an untyped constant is bool, rune, +int, float64, complex128 or string +respectively, depending on whether it is a boolean, rune, integer, floating-point, +complex, or string constant. +

+

There are no constants denoting the IEEE-754 infinity and not-a-number values, but the math package's @@ -1882,9 +1893,10 @@ func (tz TimeZone) String() string {

Variable declarations

-A variable declaration creates a variable, binds an identifier to it and -gives it a type and optionally an initial value. +A variable declaration creates one or more variables, binds corresponding +identifiers to them, and gives each a type and an initial value.

+ 
 VarDecl     = "var" ( VarSpec | "(" { VarSpec ";" } ")" ) .
 VarSpec     = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) .
@@ -1905,22 +1917,27 @@ var _, found = entries[name]  // map lookup; only interested in "found"
 
 

 If a list of expressions is given, the variables are initialized
-by assigning the expressions to the variables
-in order; all expressions must be consumed and all variables initialized from them.
+with the expressions following the rules for assignments.
 Otherwise, each variable is initialized to its zero value.
 

 
 

-If the type is present, each variable is given that type.
-Otherwise, the types are deduced from the assignment
-of the expression list.
+If a type is present, each variable is given that type.
+Otherwise, each variable is given the type of the corresponding
+initialization value in the assignment.
+If that value is an untyped constant, it is first
+converted to its default type;
+if it is an untyped boolean value, it is first converted to type bool.
+The predeclared value nil cannot be used to initialize a variable
+with no explicit type.
 

 
-

-If the type is absent and the corresponding expression evaluates to an
-untyped constant, the type of the declared variable
-is as described in ยงAssignments.
-

+
+var d = math.Sin(0.5)  // d is int64
+var i = 42             // i is int
+var t, ok = x.(T)      // t is T, ok is bool
+var n = nil            // illegal
+

 
 

 Implementation restriction: A compiler may make it illegal to declare a variable
@@ -4318,7 +4335,7 @@ a[i] = 23
 
 

 An assignment operation x op=
-y where op is a binary arithmetic operation equivalent
+y where op is a binary arithmetic operation is equivalent
 to x = x op
 y but evaluates x
 only once.  The op= construct is a single token.
@@ -4336,8 +4353,8 @@ i &^= 1<<n
 A tuple assignment assigns the individual elements of a multi-valued
 operation to a list of variables.  There are two forms.  In the
 first, the right hand operand is a single multi-valued expression
-such as a function evaluation or channel or
-map operation or a type assertion.
+such as a function call, a channel or
+map operation, or a type assertion.
 The number of operands on the left
 hand side must match the number of values.  For instance, if
 f is a function returning two values,
@@ -4411,23 +4428,21 @@ to the type of the operand to which it is assigned, with the following special c
 

 
 
    
-
  1. 
-	If an untyped constant
-	is assigned to a variable of interface type or the blank identifier,
-	the constant is first converted to type
-	bool, rune, int, float64,
-	complex128 or string respectively, depending on
-	whether the value is a boolean, rune, integer, floating-point, complex, or
-	string constant.
-
    2. 
+
  2. 
+	Any typed value may be assigned to the blank identifier.
+
    3. 
 
-
  3. 
-	
-	If a left-hand side is the blank identifier, any typed or non-constant
-	value except for the predeclared identifier
-	nil
-	may be assigned to it.
-
    4. 
+
  4. 
+	If an untyped constant
+	is assigned to a variable of interface type or the blank identifier,
+	the constant is first converted to its
+	 default type.
+
    5. 
+
+
  5. 
+	If an untyped boolean value is assigned to a variable of interface type or
+	the blank identifier, it is first converted to type bool.
+
    6. 
 

 
 
If statements