iOS OC实现map、filter、reduce等高阶函数

在 Swift 中，map filter reduce 等高阶函数的存在可以让我们更快的处理数据。
在OC中实现对应方法：

• map：处理数组中的每个元素，并返回一个新的结果数组。

- (NSArray *)_map:(id(^)(id))hanlde {
    if (!hanlde || !self) return self;
    
    NSMutableArray *arr = NSMutableArray.array;
    for (id obj in self) {
        id new = hanlde(obj);
        [arr addObject:new];
    }
    return arr.copy;
}


/** Usages: */
NSArray *languages = @[@"objctive-c", @"java", @"swift",@"javascript", @"php"];
languages = [languages _map:^id _Nonnull(NSString *obj) {
  return [obj stringByAppendingString:@" !!"];
}];

NSLog(@"%@", languages);
/** Prints
(
    "objctive-c !!",
    "java !!",
    "swift !!",
    "javascript !!",
    "php !!"
)
*/

• filter：按照规则返回过滤之后的数组

- (NSArray *)_filter:(BOOL(^)(id))handle {
    if (!handle || !self) return self;
    
    NSMutableArray *arr = NSMutableArray.array;
    for (id obj in self) {
        if (handle(obj)) {
            [arr addObject:obj];
        }
    }
    return arr.copy;
}


/** Usages: */
NSArray *numbers = @[@1,@2,@5,@11,@6,@0,@3];
NSArray *oddArr = [numbers _filter:^BOOL(NSNumber *obj) {
  return (obj.intValue %2 != 0);
}];
    
NSLog(@"%@", oddArr);
/** Prints
(
    1,
    5,
    11,
    3
)
*/

• reduce：按照规则将组内元素一一合并，返回最终结果

- (id)_reduce:(id(^)(id, id))handle initial:(id)initial {
    if (!handle || !self || !initial) return self;
    if (self.count <1) return initial;
    
    id value = initial;
    for (id obj in self) {
        value = handle(value, obj);
    }
    return value;
}


/** Usages: */
NSArray *numbers = @[@3,@2,@10];
id result = [numbers _reduce:^id _Nonnull(NSNumber *obj1, NSNumber *obj2) {
  return @(obj1.intValue * obj2.intValue);
} initial:@1];
    
NSLog(@"%@", result);
// Prints  "60"

NSArray *words = @[@"hello", @"world", @"good", @"night"];
id result = [words _reduce:^id _Nonnull(NSString *obj1, NSString *obj2) {
  return [NSString stringWithFormat:@"%@%@", obj1, obj2];
} initial:@""];
    
NSLog(@"%@", result);
// Prints "helloworldgoodnight"

• foreach：对每个元素做操作

- (void)_forEach:(void(^)(id))handle {
    if (!handle || !self) return;
    
    for (id obj in self) {
        handle(obj);
    }
}


/** Usages: */
[subviews _forEach:^(UIView *view) {
  [view removeFromSuperview];
}];

可改进：函数式调用
难点：获取 block 签名函数