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revert specification of pointer types to current implementation

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(do not allow explicit type forward declarations) and more clearly
specify resolution

R=r
DELTA=30  (9 added, 7 deleted, 14 changed)
OCL=13967
CL=13987
This commit is contained in:
Robert Griesemer 2008-08-07 17:15:10 -07:00
parent 69353f0a50
commit e3fc124640
1 changed files with 22 additions and 20 deletions
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42
doc/go_lang.txt
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@ -4,7 +4,7 @@ The Go Programming Language (DRAFT)
Robert Griesemer, Rob Pike, Ken Thompson
----
(August 4, 2008)
(August 7, 2008)
This document is a semi-formal specification/proposal for a new
systems programming language. The document is under active
@ -709,33 +709,33 @@ key-value pairs separated by a colon:
TODO: helper syntax for nested arrays etc? (avoids repeating types but
complicates the spec needlessly.)
Pointer types
----
Pointer types are similar to those in C.
PointerType = "*" Type.
PointerType = "*" ElementType.
Pointer arithmetic of any kind is not permitted.
*int
*map[string] *chan
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:
For pointer types (only), the pointer element type may be an
identifier referring to an incomplete (not yet fully defined) or undeclared
type. This allows the construction of recursive and mutually recursive types
such as:
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, all forward-declared types must be
fully declared if they are used.
If the element type is an undeclared identifier, the declaration implicitly
forward-declares an (incomplete) type with the respective name. By the end
of the package source, any such forward-declared type must be completely
declared in the same or an outer scope.
Channel types
@ -1059,26 +1059,28 @@ TODO move/re-arrange section on iota.
Type declarations
----
A type declaration introduces a name as a shorthand for a type. The name refers
to an incomplete type until the type specification is complete. If no type is
provided at all, the declaration effectively serves as a forward declaration.
Incomplete types can be used together (and only) with pointer types.
A type declaration introduces a name as a shorthand for a type.
TypeDecl = "type" ( TypeSpec | "(" TypeSpecList [ ";" ] ")" ).
TypeSpec = identifier [ Type ] .
TypeSpec = identifier Type .
TypeSpecList = TypeSpec { ";" TypeSpec }.
The name refers to an incomplete type until the type specification is complete.
Incomplete types can be referred to only by pointer types. Consequently, in a
type declaration a type may not refer to itself unless it does so with a pointer
type.
type List // forward declaration
type IntArray [16] int
type (
Point struct { x, y float };
Polar Point
)
Since incomplete types can only be used with pointer types, in a type
declaration a type may not refer to itself unless it does so with a
pointer type.
type TreeNode struct {
left, right *TreeNode;
value Point;
}
Variable declarations