Standard function let and generic extension function in kotlin

fun main() {
    "yuknight".mLet {
        it
        true
        "Ok"
    }
    123.mLet {
        it
    }

    val str = "str".let {
        it
    }

}

//fun<I, O>  In the function , Declare two generics , Function type ,I Input parameters ,O Function return value 
//I.mLet  Yes I Input parameters for extension , The extension function name is mLet, It means that all types can call this function 
//lambda:(I)->O  (I Input parameters )->O Return value 
//:O   The return value of the function will change according to the user's return type 
//lambda(this)  I Function extension , In the whole extension function ,this == I  Oneself 
private inline fun <I, O> I.mLet(lambda: (I) -> O) = lambda(this)
/**
 * private inline fun <I, O> I.mLet(lambda: (I) -> O): O {
 *        lambda(this)
 * }
 */
//let  Function source code 
/**
 * public inline fun <T, R> T.let(block: (T) -> R): R {
 *     return block(this)
 *  }
 */