objective-c blocks Practice

gistfile1.m

NSArray *before = @[ @"hoge", @"fuga", @"piyo", @1, @2, @3, @"foo", @"bar"];
NSArray *after = [before grep:^BOOL(id obj) {return [obj isKindOfClass:[NSString class]];}];
NSLog(@"%@", after);

NSArray+grep.h

#import <Foundation/Foundation.h>

@interface NSArray (grep)
- (NSArray *)grep:(BOOL(^)(id))block;
@end

NSArray+grep.m

#import "NSArray+grep.h"

@implementation NSArray (grep)

- (NSArray *)grep:(BOOL(^)(id))block
{
    NSMutableArray *newArray = [NSMutableArray array];
    [self enumerateObjectsUsingBlock:^(id item,NSUInteger idx,BOOL *stop){
        //引数で渡されたblockを実行して戻り値のBOOLを格納
        BOOL obj = block(item);
        //blockの実行結果が真なら配列に追加
        if (obj) {
            [newArray addObject:item];
        }
    }];
    return newArray;  
}

@end