Default values for function parameters

import ballerina/io;

// Use the value of the preceding `str` parameter to initialize the `end` parameter.
function subString(string str, int 'start = 0, int end = str.length()) returns string {
    return str.substring('start, end);
}

public function main() {
    // Call the `subString` function using the default values of `start` and `end` parameters.
    io:println(subString("Ballerina Language"));

    // Call the `subString` function by passing a value for the `start` default parameter.
    io:println(subString("Ballerina Language", 10));

    // Call the `subString` function by passing values for `start` and `end` default parameters.
    io:println(subString("Ballerina Language", 10, 14));
}