- 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) {...};
