defer statement

R=r
DELTA=30  (26 added, 0 deleted, 4 changed)
OCL=23533
CL=23569

diff --git a/doc/go_spec.txt b/doc/go_spec.txt
index 9a10a5435d4aa8d35c0d309c31c5f37c1e73a230..b5dd2b462158bd0681f97adc7d7567638b9a9c1a 100644 (file)
--- a/doc/go_spec.txt
+++ b/doc/go_spec.txt
@@ -3,7 +3,7 @@ The Go Programming Language Specification (DRAFT)
 
 Robert Griesemer, Rob Pike, Ken Thompson
 
-(January 23, 2009)
+(January 26, 2009)
 
 ----
 
@@ -235,6 +235,7 @@ Contents
                Continue statements
                Label declaration
                Goto statements
+               Defer statements
 
        Function declarations
                Method declarations
@@ -682,8 +683,8 @@ Reserved words
 The following words are reserved and must not be used as identifiers:
 
        break        default      func         interface    select
-       case         else         go           map          struct
-       chan                                      goto         package      switch
+       case         defer        go           map          struct
+       chan         else         goto         package      switch
        const        fallthrough  if           range        type
        continue     for          import       return       var
 
@@ -2501,7 +2502,8 @@ Statements control execution.
        Statement =
                Declaration | LabelDecl | EmptyStat |
                SimpleStat | GoStat | ReturnStat | BreakStat | ContinueStat | GotoStat |
-               FallthroughStat | Block | IfStat | SwitchStat | SelectStat | ForStat .
+               FallthroughStat | Block | IfStat | SwitchStat | SelectStat | ForStat |
+               DeferStat .
 
        SimpleStat =
                ExpressionStat | IncDecStat | Assignment | SimpleVarDecl .
@@ -3015,6 +3017,30 @@ clause of the switch statement.
        FallthroughStat = "fallthrough" .
 
 
+Defer statements
+----
+
+A defer statement invokes a function whose execution is deferred to the moment
+when the surrounding function returns.
+
+       DeferStat = "defer" Expression .
+
+The expression must be a function call. Each time the defer statement executes,
+the parameters to the function call are evaluated and saved anew but the
+function is not invoked. Immediately before the innermost function surrounding
+the defer statement returns, but after its return value (if any) is evaluated,
+each deferred function is executed with its saved parameters. Deferred functions
+are executed in LIFO order.
+
+       lock(l);
+       defer unlock(l);  // unlocking happens before surrounding function returns
+
+       // prints 3 2 1 0 before surrounding function returns
+       for i := 0; i <= 3; i++ {
+               defer print(i);
+       }
+
+
 ----
 
 Function declarations