Add select statement
SVN=114147
diff --git a/doc/go_lang.txt b/doc/go_lang.txt
index d30675e..319de95 100644
--- a/doc/go_lang.txt
+++ b/doc/go_lang.txt
@@ -1163,7 +1163,7 @@
[ LabelDecl ] ( StructuredStat | UnstructuredStat ) .
StructuredStat =
- Block | IfStat | SwitchStat | ForStat | RangeStat .
+ Block | IfStat | SwitchStat | SelectStat | ForStat | RangeStat .
UnstructuredStat =
Declaration | SimpleVarDecl |
@@ -1399,6 +1399,65 @@
}
+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: type switch?
-- TODO: select
- TODO: words about slices
- TODO: what is nil? do we type-test by a nil conversion or something else?
