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mirror of https://github.com/golang/go synced 2024-11-21 21:14:47 -07:00

1) Fixed spec w/ respect to result types.

2) Added proposal for making "if" statements consistent with the
   other control structures.

R=r
DELTA=59  (32 added, 6 deleted, 21 changed)
OCL=15583
CL=15964
This commit is contained in:
Robert Griesemer 2008-09-26 11:15:14 -07:00
parent 2c52881a85
commit ac05579345

View File

@ -4,7 +4,7 @@ The Go Programming Language Specification (DRAFT)
Robert Griesemer, Rob Pike, Ken Thompson
----
(September 19, 2008)
(September 26, 2008)
This document is a semi-formal specification of the Go systems
@ -19,8 +19,6 @@ Any part may change substantially as design progresses.
<!--
Open issues according to gri:
[ ] clarification on interface types, rules
[ ] methods for all types
[x] remove "any"
[ ] convert should not be used for composite literals anymore,
in fact, convert() should go away
[ ] syntax for var args
@ -34,13 +32,10 @@ Open issues according to gri:
[ ] new(arraytype, n1, n2): spec only talks about length, not capacity
(should only use new(arraytype, n) - this will allow later
extension to multi-dim arrays w/o breaking the language)
[x] & needed to get a function pointer from a function? (NO - there is the "func" keyword - 9/19/08)
[ ] comparison operators: can we compare interfaces?
[ ] optional semicolons: too complicated and unclear
[ ] like to have assert() in the language, w/ option to disable code gen for it
[ ] composite types should uniformly create an instance instead of a pointer
[x] func literal like a composite type - should probably require the '&' to get
address
[ ] meaning of nil
[ ] clarify slice rules
[ ] something on tuples?
@ -52,12 +47,21 @@ Open issues according to gri:
[ ] iant suggests to use abstract/precise int for len(), cap() - good idea
(issue: what happens in len() + const - what is the type?)
[ ] Do composite literals create a new literal each time (gri thinks yes)
[x] should binary <- be at lowest precedence level? when is a send/receive non-blocking? (NO - 9/19/08)
[ ] consider syntactic notation for composite literals to make them parseable w/o type information
[ ] nil and interfaces - can we test for nil, what does it mean, etc.
Decisions in need of integration into the doc:
[ ] pair assignment is required to get map, and receive ok.
Closed issues:
[x] remove "any"
[x] methods for all types
[x] should binary <- be at lowest precedence level? when is a send/receive non-blocking? (NO - 9/19/08)
[x] func literal like a composite type - should probably require the '&' to get address (NO)
[x] & needed to get a function pointer from a function? (NO - there is the "func" keyword - 9/19/08)
-->
Contents
@ -1098,30 +1102,39 @@ Function types
----
A function type denotes the set of all functions with the same parameter
list and result.
and result types.
FunctionType = "(" [ ParameterList ] ")" [ Result ] .
ParameterList = ParameterSection { "," ParameterSection } .
ParameterSection = IdentifierList Type .
ParameterSection = [ IdentifierList ] Type .
Result = Type | "(" ParameterList ")" .
Functions can return multiple values simultaneously.
In ParameterList, the parameter names (IdentifierList) either must all be
present, or all be absent. If the parameters are named, each name stands
for one parameter of the specified type. If the parameters are unnamed, each
type stands for one parameter of that type.
// Function types
()
(x int)
() int
(s string)
(string)
(a, b int, z float) bool
(a, b int, z float) (bool)
(a, b int, z float) (success bool)
(a, b int, z float) (success bool, result float)
(int, int, float) (float, *[]int)
A variable can hold only a pointer to a function, not a function value.
In particular, v := func() {} creates a variable of type *(). To call the
function referenced by v, one writes v(). It is illegal to dereference a
function pointer.
TODO: For consistency, we should require the use of & to get the pointer to
a function: &func() {}.
Type equality: Two function types are equal if both have the same number
of parameters and result values and if corresponding parameter and result
types are equal. In particular, the parameter and result names are ignored
for the purpose of type equivalence.
Assignment compatibility: A function pointer can be assigned to a function
(pointer) variable only if both function types are equal.
Interface types
@ -1853,12 +1866,12 @@ In assignments, the type of the expression must match the type of the left-hand
If statements
----
If statements have the traditional form except that the
condition need not be parenthesized and the "then" statement
must be in brace brackets. The condition may be omitted, in which
case it is assumed to have the value "true".
If statements specify the conditional execution of two branches; the "if"
and the "else" branch. If Expression evaluates to true,
the "if" branch is executed. Otherwise the "else" branch is executed if present.
If Condition is omitted, it is equivalent to true.
IfStat = "if" [ [ Simplestat ] ";" ] [ Condition ] Block [ "else" Statement ] .
IfStat = "if" [ [ Simplestat ] ";" ] [ Expression ] Block [ "else" Statement ] .
if x > 0 {
return true;
@ -1877,13 +1890,26 @@ the variable is initialized once before the statement is entered.
}
TODO: We should fix this and move to:
<!--
TODO: gri thinks that Statement needs to be changed as follows:
IfStat =
"if" [ [ Simplestat ] ";" ] [ Condition ] Block
{ "else" "if" Condition Block }
[ "else" Block ] .
"if" [ [ Simplestat ] ";" ] [ Expression ] Block
[ "else" ( IfStat | Block ) ] .
To facilitate the "if else if" code pattern, if the "else" branch is
simply another "if" statement, that "if" statement may be written
without the surrounding Block:
if x > 0 {
return 0;
} else if x > 10 {
return 1;
} else {
return 2;
}
-->
Switch statements
----