Using in operator to compare string with range of strings

Question

I am using in operator to check whether a value is in range. But I am not able to understand exactly how the comparison with range of strings is done. Below are the few arguments and their output which I have tried:

   println("KOTLIN" in "J".."K")
false

   println("KOTLIN" in "Java".."Scala")
true

    println("KOTLIN" in "Java".."Bhuv")
false

Answer 1

in is compiled down to the following function (defined in kotlin.ranges.Range.kt):

public operator fun contains(value: T): Boolean = value >= start && value <= endInclusive

So "KOTLIN" in "J".."K" results in:

("J".."K").contains("KOTLIN")

The comparison in this case relies on normal String comparisons since >= and <= are compiled down to variations of compareTo. The implementation looks as follows:

public int compareTo(String anotherString) {
    int len1 = value.length;
    int len2 = anotherString.value.length;
    int lim = Math.min(len1, len2);
    char v1[] = value;
    char v2[] = anotherString.value;

    int k = 0;
    while (k < lim) {
        char c1 = v1[k];
        char c2 = v2[k];
        if (c1 != c2) {
            return c1 - c2;
        }
        k++;
    }
    return len1 - len2;
}

So, "KOTLIN" in "Java".."Scala" is equal to the following:

"KOTLIN".compareTo("Java") >=0 && "KOTLIN".compareTo("Scala") <= 0