mirror of
https://github.com/golang/go
synced 2024-09-04 15:34:21 +00:00
Add select statement
SVN=114147
This commit is contained in:
parent
e118551c29
commit
8c1408dd8e
|
@ -1163,7 +1163,7 @@ Statements control execution.
|
|||
[ LabelDecl ] ( StructuredStat | UnstructuredStat ) .
|
||||
|
||||
StructuredStat =
|
||||
Block | IfStat | SwitchStat | ForStat | RangeStat .
|
||||
Block | IfStat | SwitchStat | SelectStat | ForStat | RangeStat .
|
||||
|
||||
UnstructuredStat =
|
||||
Declaration | SimpleVarDecl |
|
||||
|
@ -1399,6 +1399,65 @@ If the expression is omitted, it is equivalent to "true".
|
|||
}
|
||||
|
||||
|
||||
Select statements
|
||||
----
|
||||
|
||||
A select statement chooses which of a set of possible communications
|
||||
will proceed. It looks similar to a switch statement but with the
|
||||
cases all referring to communication operations.
|
||||
|
||||
SelectStat = "select" "{" { CommClause } "}" .
|
||||
CommClause = CommCase { Statement } .
|
||||
CommCase = ( "default" | ( "case" ( SendCase | RecvCase) ) ) ":" .
|
||||
SendCase = Send .
|
||||
RecvCase = [ identifier '=' ] RecvExpression .
|
||||
RecvExpression = '<' Expression .
|
||||
|
||||
The select statement evaluates all the channel (pointers) involved.
|
||||
If any of the channels can proceed, the corresponding communication
|
||||
and statements are evaluated. Otherwise, if there is a default case,
|
||||
that executes; if not, the statement blocks until one of the
|
||||
communications can complete. A channel pointer may be nil, which is
|
||||
equivalent to that case not being present in the select statement.
|
||||
|
||||
If the channel sends or receives "any" or an interface type, its
|
||||
communication can proceed only if the type of the communication
|
||||
clause matches that of the dynamic value to be exchanged.
|
||||
|
||||
If multiple cases can proceed, a uniform fair choice is made regarding
|
||||
which single communication will execute.
|
||||
|
||||
var c, c1, c2 *chan int;
|
||||
select {
|
||||
case i1 = <c1:
|
||||
printf("received %d from c1\n", i1);
|
||||
case >c2 = i2:
|
||||
printf("sent %d to c2\n", i2);
|
||||
default:
|
||||
printf("no communication\n");
|
||||
}
|
||||
|
||||
for { // send random sequence of bits to c
|
||||
select {
|
||||
case >c = 0: // note: no statement, no fallthrough, no folding of cases
|
||||
case >c = 1:
|
||||
}
|
||||
}
|
||||
|
||||
var ca *chan any;
|
||||
var i int;
|
||||
var f float;
|
||||
select {
|
||||
case i = <ca:
|
||||
printf("received int %d from ca\n", i);
|
||||
case f = <ca:
|
||||
printf("received float %f from ca\n", f);
|
||||
}
|
||||
|
||||
TODO: do we allow case i := <c: ?
|
||||
TODO: need to precise about all the details but this is not the right doc for that
|
||||
|
||||
|
||||
For statements
|
||||
----
|
||||
|
||||
|
@ -1591,7 +1650,6 @@ TODO
|
|||
----
|
||||
|
||||
- TODO: type switch?
|
||||
- TODO: select
|
||||
- TODO: words about slices
|
||||
- TODO: what is nil? do we type-test by a nil conversion or something else?
|
||||
|
||||
|
|
Loading…
Reference in a new issue