add BlockFptr convenience function

MABlockClosure.h

@@ -17,3 +17,9 @@
 - (void *)fptr;
 
 @end
+
+// convenience function, returns a function pointer
+// whose lifetime is tied to 'block'
+// block MUST BE a heap block (pre-copied)
+// or a global block
+void *BlockFptr(id block);

MABlockClosure.m

@@ -2,6 +2,7 @@
 #import "MABlockClosure.h"
 
 #import <assert.h>
+#import <objc/runtime.h>
 #import <sys/mman.h>
 
 
@@ -286,3 +287,18 @@ - (void *)fptr
 }
 
 @end
+
+void *BlockFptr(id block)
+{
+    @synchronized(block)
+    {
+        MABlockClosure *closure = objc_getAssociatedObject(block, BlockFptr);
+        if(!closure)
+        {
+            closure = [[MABlockClosure alloc] initWithBlock: block];
+            objc_setAssociatedObject(block, BlockFptr, closure, OBJC_ASSOCIATION_RETAIN);
+            [closure release]; // retained by the associated object assignment
+        }
+        return [closure fptr];
+    }
+}

main.m

@@ -26,4 +26,9 @@ int main(int argc, char **argv)
     NSRect r = ((NSRect (*)(void))[closure fptr])();
     NSLog(@"%@", NSStringFromRect(r));
     [closure release];
+
+    block = [^(NSString *s) { return [s stringByAppendingFormat: @" %s", argv[0]]; } copy];
+    NSString *strObj = ((id (*)(id))BlockFptr(block))(@"hello");
+    NSLog(@"%@", strObj);
+    [block release];
 }