How to create extension methods in Kotlin

Question

Hello, I’m coming from C# to work with Kotlin and C# when there was any code that was used constantly, it was common to create extension methods that worked as shortcuts to it. Ex:

namespace Test
{
    public static class Test 
    {
        public static string PutDotInEndOfString(this string str) 
        {
            return str + ".";
        }
    }
}

Because of this facility, I am looking for something to (or replace or declare a new function) that can facilitate the use of simple methods like toLowerCase that currently presents me a Warning over the Locale default, ex:

class Test {
    private lateinit var str: String
    init {
        str = "TEST"
    }
    testMethod(): String {
        // return str.toLowerCase() // assim fica aparecendo o warning
        return str.toLowerCase(Locale.getDefault())
    }
}

Is there any way I can extend or overwrite the method toLowerCase in the example above so you don’t have to pass the locale every time you use it?

Answer 1

Yes, there is a feature very similar to C#. You just need to prefix the function name with the type that will receive the extension method.

You can see more about this on documentation.

fun String.myToLowerCase(): String {
    return this.toLowerCase(Locale.getDefault())
}

print("KOTLIN IS AWESOME".myToLowerCase())

^{See working}