Advanced Mac OS X Programming: The Big Nerd Ranch Guide

Block Variables

Blocks are not limited to living in-line in method or function calls. You can have variables, whether local, global, or instance, that point to blocks. The syntax is like standard C function pointer syntax but using a caret instead of a star:

v​o​i​d​ ​(​^​b​l​o​c​k​P​t​r​V​a​r​)​ ​(​N​S​S​t​r​i​n​g​ ​*​a​r​g​)​ ​=​ ​^​(​N​S​S​t​r​i​n​g​ ​*​a​r​g​)​ ​{​ ​N​S​L​o​g​ ​(​@​"​%​@​"​,​ ​a​r​g​)​;​ ​}​;​

The name of the variable is blockPtrVar. The block returns nothing (void) and takes a single NSString argument.

Invoke it like a function pointer:

b​l​o​c​k​P​t​r​V​a​r​ ​(​@​"​h​e​l​l​o​"​)​;​

which prints “hello.”

Things become more readable when you use a typedef:

t​y​p​e​d​e​f​ ​v​o​i​d​ ​(​^​B​l​o​c​k​T​y​p​e​)​ ​(​N​S​S​t​r​i​n​g​ ...