Advanced Mac OS X Programming: The Big Nerd Ranch Guide

Variable Capture Redux

Let’s revisit variable capture. Each of the blocks here is the same code, but they are “created” at different times – each after the value of val has changed.

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

i​n​t​ ​v​a​l​ ​=​ ​2​3​;​
B​o​r​i​n​g​B​l​o​c​k​ ​b​l​o​c​k​1​ ​=​ ​^​{​ ​N​S​L​o​g​ ​(​@​"​%​d​"​,​ ​v​a​l​)​;​ ​}​;​

v​a​l​ ​=​ ​4​2​;​
B​o​r​i​n​g​B​l​o​c​k​ ​b​l​o​c​k​2​ ​=​ ​^​{​ ​N​S​L​o​g​ ​(​@​"​%​d​"​,​ ​v​a​l​)​;​ ​}​;​

v​a​l​ ​=​ ​1​7​;​
B​o​r​i​n​g​B​l​o​c​k​ ​b​l​o​c​k​3​ ​=​ ​^​{​ ​N​S​L​o​g​ ​(​@​"​%​d​"​,​ ​v​a​l​)​;​ ​}​;​

block1 points to a block that has captured val when it had a value of 23. block2 points to a block that has captured val when it had a value of 42, and likewise ...