[Cotlin] I'd like to ask you about the expansion function of the Cotlin standard library (also, let, with, apply, etc.)ㅛ

inline fun <T, R> T.run(block: T.() -> R): R {
    return this.block()
}

The book says that the run extension function is defined in this way.

The explanation of this is as follows

The block parameter receives a function in the form of T.() -> R and immediately calls the run extension function, this.block() Call and pass the receiver of the run to the function indicated by the block.

In other words, when called as "Hello".run { println(this)}, the run extension function is as follows.

fun String.run(block: String.() -> Unit): Unit {
    // // block = println(this)
    return this.block()
}

What I don't understand here is... The extended function allows access to the receiver member using this inside the block

If you do it,

But here this.If you do block... I think it means calling the block() member function of the String type.

As far as I know, there is no block function inside the String class.How is this possible?

Shouldn't it just be block() from return

And if the additional question is block is String() -> Unit, shouldn't we receive the extension function of String as a parameter?

println is just println itself. How does this work?

It's very confusing