This is a block

^{    NSLog(@"This is from a block");}

a block with arguments

^(double dividend, double divisor){    double quotient = dividend/divisor;    return quotient;}

although blocks look like functions, they can be stored in variables. Like other variables, block variables are declared and then assigned values.

//declare the block variablevoid (^devowelizer) (id, NSUInteger, BOOL *);

void : return type of block

^    : indication that this is a block

devowelizer: name of block variable

comma-delimited arguments

//assign a block to the variabledevowelizer =  ^(id string, NSUInteger i, BOOL *stop){    NSMutableString *newString=[NSMutableString stringWithString:string];    for (NSString *s in vowels){        NSRange fullRange = NSMakeRange(0,[newString length]);        [newString replaceOccurrencesOfString:s                                   withString:@""                                      options:NSCaseInsensitiveSearch                                        range:fullRange];    }    [newStrings addObject:newString];};//end of block assignment

Passing in a block

Because devowelizer is a variable, you can pass it as an argument. NSArray has a method called enumerateObjectsUsingBlock: This method expects a block as its sole argument, it will execute that block once for each object in the array.

[oldStrings enumerateObjectsUsingBlock:devowelizer];

 

Add a check at the beginning of the block

devowelizer = ^(id string, NSUInteger i, BOOL *stop){    NSRange yRange = [string rangeOfString:@"y"                                       options:NSCaseInsensitiveSearch];    //did i find a y?    if(yRange.location != NSNotFound){         *stop = YES;         return;    }    ...};

typedef

Block syntax can be confusing, but you can make it friendlier using the typedef keyword.

Remember that tyepdef belongs at the top of the file or in a header, outside of any method implementations.

#import 
     
      typedef void (^ArrayEnumerateBlock)(id,NSUInteger,BOOL *); ... ArrayEnumerateBlock devowelizer;