• 局部变量：

returnType (^blockName)(parameterTypes) = ^returnType(parameters) {...};

• 属性：

@property (nonatomic, copy, nullability) returnType (^blockName)(parameterTypes);

• 方法参数：

-(void)someMethodThatTakesABlock:(returnType (^nullability)(parameterTypes))blockName;

• 方法调用参数：

[someObject someMethodThatTakesABlock:^returnType (parameters) {...}];

• typedef：

typedef returnType (^TypeName)(parameterTypes);TypeName blockName = ^returnType(parameters) {...};