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Introduced forward declaration of types per discussion with ken.

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A forward-declared (or not yet fully defined) type must be used
to construct (mutually) recursive type declarations. This simplifies
the compiler and resolves the issue at which scope the forward-
declared type is to be declared.

SVN=117770
This commit is contained in:
Robert Griesemer 2008-05-06 10:29:17 -07:00
parent f5c0763432
commit d222c65477
1 changed files with 21 additions and 10 deletions
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29
doc/go_lang.txt
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@ -1,6 +1,6 @@
The Go Programming Language
----
(April 29, 2008)
(May 5, 2008)
This document is an informal specification/proposal for a new systems programming
language.
@ -678,19 +678,26 @@ Pointer types are similar to those in C.
PointerType = "*" Type.
We do not allow pointer arithmetic of any kind.
Pointer arithmetic of any kind is not permitted.
*int
*map[string] *chan
It is legal to write a pointer type (only) such as *T or **T even if T
is not yet defined as a type name. This allows the construction of
mutually recursive data types such as structs:
It is legal to write a pointer type (only) such as *T even if T is
an incomplete type (i.e., either not yet fully defined or forward
declared). This allows the construction of recursive types such as:
type S1 struct { s2 *S2 } // S2 is not yet declared
type S struct { s *S }
Together with a type forward declaration, mutually recursive types
can be constructed such as:
type S2 // forward declaration of S2
type S1 struct { s2 *S2 }
type S2 struct { s1 *S1 }
By the end of the package source, such types must be fully declared.
By the end of the package source, all forward-declared types must be
fully declared if they are used.
There are no pointer literals.
@ -976,13 +983,17 @@ A constant declaration gives a name to the value of a constant expression.
Type declarations
----
A type declaration introduces a name as a shorthand for a type.
A type declaration introduces a name as a shorthand for a type. Providing only
a name without a type serves as a forward declaration: The name is declared and
given an incomplete type. Incomplete types can be used together (and only) with
pointer types.
TypeDecl = "type" ( TypeSpec | "(" TypeSpecList [ ";" ] ")" ).
TypeSpec = identifier Type .
TypeSpec = identifier [ Type ] .
TypeSpecList = TypeSpec { ";" TypeSpec }.
type List // foward declaration
type IntArray [16] int
type (
Point struct { x, y float };