Assign a variable inside a Block to a variable outside a Block

I'm getting an error

Variable is not assignable (missing __block type specifier)

on the line aPerson = participant;. How can I make sure the block can access the aPerson variable and the aPerson variable can be returned?

Person *aPerson = nil;

[participants enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {   
    Person *participant = (Person*)obj;

    if ([participant.gender isEqualToString:@"M"]) {
        aPerson = participant;
        *stop = YES;
    }
}];

return aPerson;

You need to use this line of code to resolve your problem:

__block Person *aPerson = nil;

For more details, please refer to this tutorial: Blocks and Variables

Just a reminder of a mistake I made myself too, the

 __block

declaration must be done when first declaring the variable, that is, OUTSIDE of the block, not inside of it. This should resolve problems mentioned in the comments about the variable not retaining its value outside of the block.

Just use the __block prefix to declare and assign any type of variable inside a block.

For example:

__block Person *aPerson = nil;

__block NSString *name = nil;

To assign a variable inside block which outside of block always use __block specifier before that variable your code should be like this:-

__block Person *aPerson = nil;