Demonstrates how -copy and -retain are handled for different block types (stack, heap, global).

block-copy.m

/*
 * Demonstrates how -copy and -retain are handled for different block types (stack, heap, global).
 */

#import <Foundation/Foundation.h>

/* print a block -description to stdout */
void PrintBlock (NSString *name, id b) {
    NSString *str;
    str = [NSString stringWithFormat: @"%@ (%@):\n\t-retain\t%@\n\t-copy\t%@\n\n", b, name, [[b retain] autorelease], [[b copy] autorelease]];
    printf("%s", [str UTF8String]);
};

int main (int argc, char *argv[]) {
    NSAutoreleasePool *pool = [NSAutoreleasePool new];

    /* Stack block */
    int captured = 1;
    PrintBlock(@"Stack", ^{ return captured; });

    /* Heap block */
    PrintBlock(@"Heap", [[^{ return captured; } copy] autorelease]);

    /* Global block */
    PrintBlock(@"Global", ^{});

    [pool drain];
    return 0;
}

Example output:

<NSStackBlock: 0x7fff5fbff580> (Stack):
-retain <NSStackBlock: 0x7fff5fbff580>
-copy <NSMallocBlock: 0x10010dd20>

<NSMallocBlock: 0x10010e910> (Heap):
-retain <NSMallocBlock: 0x10010e910>
-copy <NSMallocBlock: 0x10010e910>

<NSGlobalBlock: 0x100001140> (Global):
-retain <NSGlobalBlock: 0x100001140>
-copy <NSGlobalBlock: 0x100001140>

The take-away:

Stack Block:
-retain is a no-op
-copy returns a heap-allocated copy of the receiver

Heap Block:
-retain increments the receiver's reference count.
-copy calls -retain

Global Block (no captured variables):
-retain is a no-op
-copy is a no-op