This chapter is from the book
This chapter is from the book
This chapter is from the book
This chapter is from the book
When To Copy
So when do you need to copy a block? Make a copy whenever a block will outlive the scope it is defined in. In particular, these snippets are broken:
if (rand() % 1 == 0) {
blockPtr = ^{ NSLog (@"You are a winner!"); };
} else {
blockPtr = ^{ NSLog (@"Please try again!"); };
}
The braces for the branches of the if statement introduce a new scope, so the blocks are invalid afterwards.
blockPtr = ^{ NSLog (@"Help me"); };
return blockPtr;
Like returning the address of a local variable, returning a block that is still on the stack will cause problems later on, especially if you capture any local variables whose storage vanishes when the function ends.
BoringBlock blocks[10];
for (int i = 0; i < 10; i++) {
blocks[i] = ^{
NSLog (@"captured %d", i);
};
}
Similar to the if branches, the body of the for loop is a different scope, so the blocks are invalid once the loop ends.