How does typedef-ing a block works

问题

In C/Obj-C, we do a typedef like this typedef int MYINT; which is clear.

Doing typedef for a block -typedef void (^MyBlock) (int a);

Now, we can use MyBlock.

Shouldn't it be like - typedef void (^MyBlock) (int a) MyBlock; similar to #define?

How the syntax works?

回答1:

See Declaring a Block Reference in "Blocks Programming Topics":

Block variables hold references to blocks. You declare them using syntax similar to that you use to declare a pointer to a function, except that you use ^ instead of *.

So

 typedef void (^myBlock) (int a);

defines a the type of a block using the same syntax as

 typedef void (*myFunc) (int a);

declares a function pointer.

See e.g. Understanding typedefs for function pointers in C for more information about function pointers.

回答2:

Also from "Blocks Programming Topics", creating a type for blocks should be like this:

typedef returnType (^blockName)(argument1, argument2, ...)

Below is a very simple practical example:

typedef float (^MyBlockType)(float, float);
MyBlockType AddTwoFloat = ^(float a, float b) {return a + b;};
MyBlockType MultiplyTwoFloat = ^(float a, float b) {return a * b;};
float c = AddTwoFloat(1, 2); //c = 3
float d = MultiplyTwoFloat(1, 2); //d = 2

来源：https://stackoverflow.com/questions/15310880/how-does-typedef-ing-a-block-works