Magento 2 Plugin - What is the $subject

Question

What is the $subject in a plugin?

My code is:

 Class Product 
{
public function afterGetPrice(\Magento\Catalog\Model\Product $subject, 
$result) 
{ 

    return $result*2; 
}
} 

Answer 1

The parameter $subject is the original object or class you are writing a plugin for.

See: https://alanstorm.com/magento_2_object_manager_plugin_system/

An after plugin method has two parameters. The first ($subject above), is the object the method was called on (in our case, that’s Pulsestorm\TutorialPlugin\Model\Example\Interceptor object). The second parameter ($result above) is the result of the original method call.

Also explained here:

https://devdocs.magento.com/guides/v2.2/extension-dev-guide/plugins.html

The first argument for the before, after, and around methods is an object that provides access to all public methods of the observed method’s class.

Answer 2

Plugin concepts introduced to do some function which was declared in public methods in core functions.

getPrice() -> function available extended methods "before, after and around".

For example:

For "x" product want to add extra price while loading product page.

In our custom module will declare,

BeforeGetPrice - this method will execute before execution core Catalog Model getPrice function.

AfterGetPrice - method will execute after execution core Catalog Model getPrice function.

AroundGetPrice - execute before and after execution core Catalog Model getPrice function.

I was given simple explanation, these function have limitation please go through Magento devdocs plugin concepts.

afterGetPrice($subject, $procees)

Parameters

$subject -> denotes the public function which going to be replace or extend the parent or original Class object.

$proceed -> core function final result or return output.