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- clarified section on return statements

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- added some TODOs

DELTA=46  (15 added, 4 deleted, 27 changed)
OCL=32901
CL=32918
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Robert Griesemer 2009-08-07 17:05:41 -07:00
parent 6be0f50b97
commit 4b90833803
1 changed files with 37 additions and 26 deletions
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doc/go_spec.html
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@ -9,6 +9,10 @@ Open issues:
Todo's:
[ ] need language about function/method calls and parameter passing rules
[ ] update language with respect to forward declarations
[ ] clarify what a field name is in struct declarations
(struct{T} vs struct {T T} vs struct {t T})
[ ] need explicit language about the result type of operations
[ ] may want to have some examples for the types of shift operations
[ ] document illegality of package-external tuple assignments to structs
@ -3624,21 +3628,26 @@ and optionally provides a result value or values to the caller.
ReturnStmt = "return" [ ExpressionList ] .
</pre>
<p>
In a function without a result type, a "return" statement must not
specify any result values.
</p>
<pre>
func procedure() {
func no_result() {
return
}
</pre>
<p>
There are two ways to return values from a function with a result
type. The first is to explicitly list the return value or values
in the "return" statement.
Normally, the expressions
must be single-valued and assignment-compatible to the elements of
the result type of the function.
There are three ways to return values from a function with a result
type:
</p>
<ol>
<li>The return value or values may be explicitly listed
in the "return" statement. Each expression must be single-valued
and assignment-compatible to the corresponding element of
the result type of the function.
<pre>
func simple_f() int {
return 2
@ -3648,29 +3657,25 @@ func complex_f1() (re float, im float) {
return -7.0, -4.0
}
</pre>
<p>
However, if the expression list in the "return" statement is a single call
to a multi-valued function, the values returned from the called function
will be returned from this one. The result types of the current function
and the called function must match.
</p>
</li>
<li>The expression list in the "return" statement may be a single
call to a multi-valued function. The effect is as if each value
returned from that function were assigned to a temporary
variable with the type of the respective value, followed by a
"return" statement listing these variables, at which point the
rules of the previous case apply.
<pre>
func complex_f2() (re float, im float) {
return complex_f1()
}
</pre>
<p>
The second way to return values is to use the elements of the
result list of the function as variables. When the function begins
execution, these variables are initialized to the zero values for
their type (§The zero value). The function can assign them as
necessary; if the "return" provides no values, those of the variables
will be returned to the caller.
</p>
</li>
<li>The expression list may be empty if the functions's result
type specifies names for its result parameters (§Function Types).
The result parameters act as ordinary local variables that are
initialized to the zero values for their type (§The zero value)
and the function may assign values to them as necessary.
The "return" statement returns the values of these variables.
<pre>
func complex_f3() (re float, im float) {
re = 7.0;
@ -3678,9 +3683,15 @@ func complex_f3() (re float, im float) {
return;
}
</pre>
</li>
</ol>
<p>
TODO: Define when return is required.
<font color=red>
TODO: Define when return is required.<br />
TODO: Language about result parameters needs to go into a section on
function/method invocation<br />
</font>
</p>
<h3>Break statements</h3>