Question

I am attempting to traverse an array in order to calculate a value, modeled by the code below:

double foo = 0;

[sortedKeys enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop){
  foo += (NSNumber*)[obj doSomething].doubleValue
}];

However I get an error that foo is not scoped appropriately, how can I set foo up so that the block sees it and can modify it when it runs.

Answer 1

You should add __block to the declaration in order to be able to modify a variable from inside the block:

__block double foo = 0;