Magento2 plugin around method different between callable and Closure paramters on param $proceed

Question

I have checked magento2 ,There are two types of parameters that can be sent to

around method

• \Closure $proceed example aroundSave(\Magento\Catalog\Model\Product $subject, \closure $proceed)
• callable $proceed example aroundSave(\Magento\Catalog\Model\Product $subject, \callable $proceed)

Now my question:

1. What is different between closure and callable?
2. Why use we define type two different types for $proceed parameter?
3. What are use of this two types parameters?

Can any describe it details

Answer 1

You have an answer here : https://stackoverflow.com/a/29730810/4629261

The difference is, that a [Closure] must be an anonymous function, where [callable] also can be a normal function.

You can see/test this with the example below and you will see that you will get an error for the first one:

function callFunc1(Closure $closure) {
    $closure();
}

function callFunc2(Callable $callback) {
    $callback();
}

function xy() {
    echo 'Hello, World!';
}

callFunc1("xy"); // Catchable fatal error: Argument 1 passed to callFunc1() must be an instance of Closure, string given
callFunc2("xy"); // Hello, World!

So if you only want to type hint anonymous function use: Closure and if you want also to allow normal functions use callable as type hint.

http://php.net/manual/en/class.closure.php

http://php.net/manual/en/language.types.callable.php

In the Magento doc, they suggest to use [callable]

Before the list of the original method’s arguments, around methods receive a callable that will allow a call to the next method in the chain. When the callable is called, the next plugin or the observed function is called.

When you wrap a method which accepts arguments, your plugin must also accept those arguments and you must forward them when you invoke the proceed callable.

http://devdocs.magento.com/guides/v2.0/extension-dev-guide/plugins.html#defining-a-plugin