Kotlin compareTo() and comparison operators


#1

When I want to inspect the comparison operator “<” in IDEA I found the source code defined in the primitive.kt is
/**
* Compares this value with the specified value for order.
* Returns zero if this value is equal to the specified other value, a negative number if it’s less than other,
* or a positive number if it’s greater than other.
*/
public override operator fun compareTo(other: Int): Int

but actually the return type is Boolean
val n:Boolean = a < b

I am a bit confuse here, can someone give some explanation?


#2

This is an “operator” function, as seen by the operator flag. There is a fixed set of operator functions that can be implemented. They come with a special meaning.

In th case of compareTo operator, the special meaning is that the expression a<b will be translated by the compiler to the expression a.compareTo(b)<0.

You can also implement your own compareTo operator function, and so make the operator available for your own types.


#3

You saved me from my confusion.THX


#4

This correct answer.


#5

Just addition thought…

The operator compareTo(b) is used not only for <, but all other comparing operators too. This is the reason the function defined in this way.