[kotlin puzzle] what happens if you overload an arithmetic operator in the kotlin class and declare the operator as an extension function?

stay Kotlin Class overloads an arithmetic operator , And declare the operator as an extension function ？

example

Call at this time ’+' Operator

An error is as follows

Interpret errors Because the receiver type cannot be matched, the applicable... Cannot be found from the candidate methods

Analyze errors

Analyze three different ways of overloading plus function

The first one is ： Overload in the form of standard extension functions plus function

hold kotlin Decompile the code into java Code

After decompilation, we can find that plus Function in PointKt Class , This is also in line with what we said in the previous chapter “ Extension functions are not part of a class , It's declared outside the class ”, stay java In, it declares this function in a class with similar class names , And it's a static function . As an extension function plus There are two parameters ,kotlin Calling ’+' At the time java Is compiled into the following figure

The second kind ： Overloaded in the form of standard member functions plus function

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hold kotlin Decompile the code into java Code

After decompilation, we can find that as a member function plus Now there is only one parameter , and kotlin Calling ’+' At the time java Is compiled into the following figure

The third kind of ： The member function form is mixed with the extension function form

hold kotlin Decompile the code into java Code

General analysis

The first two forms are no problem , Let's look at the third usage . Put the third kind of java The code is the same as the first two java Combined with the code, we can find out some connections and differences between them

Connection and difference

It's the same as the second one plus The same function is Point Class member functions , But there are two parameters It's the same as the first one plus Like a function, it has two parameters , But none of the first plus Functional static Statement

The third compiled function is like stitching the writing methods of the first two functions . Previously, we have given the first and second methods in calling plus What a function looks like , And we can also infer the appearance of the third call ：point.plus(?,new Point(3,4)). At this point, I was thinking that since the error prompts us that the receiver type cannot match , So why can't the compiler pass itself into the function as an argument ？ I can try to write an operator overloaded with two parameters plus Function? ？

give the result as follows

stay kotlin This arithmetic operator can only have one parameter

I guess kotlin When calling arithmetic operators in the compiler , If it is a member function, it will only provide the writing method of one parameter , If it is an extension function, use the writing method of providing two parameters . The third way of writing plus Function is both a member function and requires two parameters , This may be the reason why the third writing method cannot run successfully

from equals Method we can see that it inherits from Any Class implementation always takes precedence over extension functions , And our situation, though not inherited from Any class , But is there a priority difference ？

The above is just my own idea , If you have different opinions, you can discuss , If there are errors, please also point out