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Test balloon: Changed the spec to see the implications of changing the
syntax of function types and making them "reference types" like slice, map, and chan. First step in Russ' proposal. DELTA=111 (32 added, 15 deleted, 64 changed) OCL=23669 CL=23964
This commit is contained in:
Robert Griesemer
parent
4a43198390
commit
2b9fe0ea24
153
doc/go_spec.txt
153
doc/go_spec.txt
@ -3,7 +3,7 @@ The Go Programming Language Specification (DRAFT)
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Robert Griesemer, Rob Pike, Ken Thompson
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(January 27, 2009)
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(January 30, 2009)
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----
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@ -1215,7 +1215,7 @@ types (§Types).
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StructType = "struct" [ "{" [ FieldDeclList ] "}" ] .
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FieldDeclList = FieldDecl { ";" FieldDecl } [ ";" ] .
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FieldDecl = (IdentifierList CompleteType | TypeName) [ Tag ] .
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Tag = string_lit .
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Tag = StringLit .
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// An empty struct.
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struct {}
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@ -1225,7 +1225,7 @@ types (§Types).
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x, y int;
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u float;
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A *[]int;
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F *();
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F func();
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}
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A struct may contain ``anonymous fields'', which are declared with a type
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@ -1326,9 +1326,10 @@ Function types
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----
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A function type denotes the set of all functions with the same parameter
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and result types.
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and result types, and the value "nil".
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FunctionType = "(" [ ParameterList ] ")" [ Result ] .
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FunctionType = "func" Signature .
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Signature = "(" [ ParameterList ] ")" [ Result ] .
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ParameterList = ParameterDecl { "," ParameterDecl } .
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ParameterDecl = [ IdentifierList ] ( Type | "..." ) .
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Result = Type | "(" ParameterList ")" .
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@ -1345,22 +1346,32 @@ no additional arguments). If the parameters are named, the identifier
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list immediately preceding "..." must contain only one identifier (the
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name of the last parameter).
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()
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(x int)
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() int
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(string, float, ...)
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(a, b int, z float) bool
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(a, b int, z float) (bool)
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(a, b int, z float, opt ...) (success bool)
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(int, int, float) (float, *[]int)
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func ()
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func (x int)
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func () int
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func (string, float, ...)
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func (a, b int, z float) bool
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func (a, b int, z float) (bool)
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func (a, b int, z float, opt ...) (success bool)
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func (int, int, float) (float, *[]int)
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A variable can hold only a pointer to a function, not a function value.
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In particular, v := func() {} creates a variable of type *(). To call the
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function referenced by v, one writes v(). It is illegal to dereference a
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function pointer.
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If the result type of a function is itself a function type, the result type
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must be parenthesized to resolve a parsing ambiguity:
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Assignment compatibility: A function pointer can be assigned to a function
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(pointer) variable only if both function types are equal.
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func (n int) (func (p* T))
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Assignment compatibility: A function can be assigned to a function
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variable only if both function types are equal.
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Comparisons: A variable of function type can be compared against "nil" with the
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operators "==" and "!=" (§Comparison operators). The variable is
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"nil" only if "nil" is assigned explicitly to the variable (§Assignments), or
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if the variable has not been modified since creation (§Program initialization
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and execution).
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Two variables of equal function type can be tested for equality with the
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operators "==" and "!=" (§Comparison operators). The variables are equal
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if they refer to the same function.
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Interface types
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@ -1372,7 +1383,7 @@ the set of methods specified by the interface type, and the value "nil".
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InterfaceType = "interface" [ "{" [ MethodSpecList ] "}" ] .
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MethodSpecList = MethodSpec { ";" MethodSpec } [ ";" ] .
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MethodSpec = IdentifierList FunctionType .
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MethodSpec = IdentifierList Signature .
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// An interface specifying a basic File type.
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interface {
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@ -1704,8 +1715,8 @@ For instance, given the declarations
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T1 []string
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T2 struct { a, b int };
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T3 struct { a, c int };
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T4 *(int, float) *T0
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T5 *(x int, y float) *[]string
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T4 func (int, float) *T0
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T5 func (x int, y float) *[]string
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)
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these are some types that are equal
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@ -1759,7 +1770,8 @@ Operands denote the elementary values in an expression.
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Operand = Literal | QualifiedIdent | "(" Expression ")" .
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Literal = BasicLit | CompositeLit | FunctionLit .
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BasicLit = int_lit | float_lit | char_lit | string_lit .
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BasicLit = int_lit | float_lit | char_lit | StringLit .
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StringLit = string_lit { string_lit } .
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Constants
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@ -1848,15 +1860,15 @@ A function literal represents an anonymous function. It consists of a
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specification of the function type and the function body. The parameter
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and result types of the function type must all be complete types (§Types).
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FunctionLit = "func" FunctionType Block .
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FunctionLit = "func" Signature Block .
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Block = "{" [ StatementList ] "}" .
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The type of a function literal is a pointer to the function type.
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The type of a function literal is the function type specified.
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func (a, b int, z float) bool { return a*b < int(z); }
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A function literal can be assigned to a variable of the
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corresponding function pointer type, or invoked directly.
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corresponding function type, or invoked directly.
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f := func(x, y int) int { return x + y; }
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func(ch chan int) { ch <- ACK; } (reply_chan)
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@ -2073,7 +2085,9 @@ TODO add examples
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Calls
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----
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Given a function pointer, one writes
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TODO: This needs to be expanded and cleaned up.
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Given a function or a function variable p, one writes
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p()
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@ -2083,7 +2097,7 @@ A method is called using the notation
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receiver.method()
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where receiver is a value of the receive type of the method.
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where receiver is a value of the receiver type of the method.
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For instance, given a *Point variable pt, one may call
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@ -2357,26 +2371,11 @@ Address operators
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TODO: Need to talk about unary "*", clean up section below.
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Given a function f, declared as
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TODO: This text needs to be cleaned up and go elsewhere, there are no address
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operators involved.
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func f(a int) int;
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taking the address of f with the expression
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&f
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creates a pointer to the function that may be stored in a value of type pointer
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to function:
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var fp *(a int) int = &f;
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The function pointer may be invoked with the usual syntax; no explicit
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indirection is required:
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fp(7)
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Methods are a form of function, and the address of a method has the type
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pointer to function. Consider the type T with method M:
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Methods are a form of function, and a method ``value'' has a function type.
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Consider the type T with method M:
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type T struct {
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a int;
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@ -2384,45 +2383,62 @@ pointer to function. Consider the type T with method M:
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func (tp *T) M(a int) int;
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var t *T;
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To construct the address of method M, one writes
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To construct the value of method M, one writes
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&t.M
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t.M
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using the variable t (not the type T). The expression is a pointer to a
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function, with type
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using the variable t (not the type T).
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TODO: It makes perfect sense to be able to say T.M (in fact, it makes more
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sense then t.M, since only the type T is needed to find the method M, i.e.,
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its address). TBD.
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*(t *T, a int) int
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The expression t.M is a function value with type
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and may be invoked only as a function, not a method:
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func (t *T, a int) int
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var f *(t *T, a int) int;
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f = &t.M;
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and may be invoked only as a function, not as a method:
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var f func (t *T, a int) int;
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f = t.M;
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x := f(t, 7);
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Note that one does not write t.f(7); taking the address of a method demotes
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Note that one does not write t.f(7); taking the value of a method demotes
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it to a function.
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In general, given type T with method M and variable t of type *T,
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In general, given type T with method M and variable t of type T,
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the method invocation
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t.M(args)
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is equivalent to the function call
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(&t.M)(t, args)
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(t.M)(t, args)
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If T is an interface type, the expression &t.M does not determine which
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TODO: should probably describe the effect of (t.m) under §Expressions if t.m
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denotes a method: Effect is as described above, converts into function.
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If T is an interface type, the expression t.M does not determine which
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underlying type's M is called until the point of the call itself. Thus given
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T1 and T2, both implementing interface I with interface M, the sequence
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var t1 *T1;
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var t2 *T2;
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var i I = t1;
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m := &i.M;
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m(t2);
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m := i.M;
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m(t2, 7);
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will invoke t2.M() even though m was constructed with an expression involving
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t1.
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t1. Effectively, the value of m is a function literal
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func (recv I, a int) {
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recv.M(a);
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}
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that is automatically created.
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TODO: Document implementation restriction: It is illegal to take the address
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of a result parameter (e.g.: func f() (x int, p *int) { return 2, &x }).
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(TBD: is it an implementation restriction or fact?)
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Communication operators
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@ -2643,7 +2659,7 @@ and the "else" branch. If Expression evaluates to true,
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the "if" branch is executed. Otherwise the "else" branch is executed if present.
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If Condition is omitted, it is equivalent to true.
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IfStat = "if" [ [ Simplestat ] ";" ] [ Expression ] Block [ "else" Statement ] .
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IfStat = "if" [ [ SimpleStat ] ";" ] [ Expression ] Block [ "else" Statement ] .
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if x > 0 {
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return true;
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@ -2666,7 +2682,7 @@ the variable is initialized once before the statement is entered.
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TODO: gri thinks that Statement needs to be changed as follows:
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IfStat =
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"if" [ [ Simplestat ] ";" ] [ Expression ] Block
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"if" [ [ SimpleStat ] ";" ] [ Expression ] Block
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[ "else" ( IfStat | Block ) ] .
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To facilitate the "if else if" code pattern, if the "else" branch is
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@ -2688,7 +2704,7 @@ Switch statements
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Switches provide multi-way execution.
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SwitchStat = "switch" [ [ Simplestat ] ";" ] [ Expression ] "{" { CaseClause } "}" .
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SwitchStat = "switch" [ [ SimpleStat ] ";" ] [ Expression ] "{" { CaseClause } "}" .
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CaseClause = SwitchCase ":" [ StatementList ] .
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SwitchCase = "case" ExpressionList | "default" .
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@ -3069,9 +3085,9 @@ Function declarations
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A function declaration binds an identifier to a function.
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Functions contain declarations and statements. They may be
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recursive. Except for forward declarations (see below), the parameter
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and result types of the function type must all be complete types (§Type declarations).
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and result types of the signature must all be complete types (§Type declarations).
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FunctionDecl = "func" identifier FunctionType [ Block ] .
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FunctionDecl = "func" identifier Signature [ Block ] .
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func min(x int, y int) int {
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if x < y {
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@ -3102,7 +3118,7 @@ it is declared within the scope of that type (§Type declarations). If the
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receiver value is not needed inside the method, its identifier may be omitted
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in the declaration.
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MethodDecl = "func" Receiver identifier FunctionType [ Block ] .
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MethodDecl = "func" Receiver identifier Signature [ Block ] .
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Receiver = "(" [ identifier ] [ "*" ] TypeName ")" .
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All methods bound to a receiver base type must have the same receiver type:
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@ -3296,6 +3312,7 @@ through an import declaration:
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ImportDecl = "import" ( ImportSpec | "(" [ ImportSpecList ] ")" ) .
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ImportSpecList = ImportSpec { ";" ImportSpec } [ ";" ] .
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ImportSpec = [ "." | PackageName ] PackageFileName .
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PackageFileName = StringLit .
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An import statement makes the exported top-level identifiers of the named
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package file accessible to this package.
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