Nil

• The nil type contains a single value, called nil, which is used to represent the absence of any other value.
• This is the only basic type which consists of a single type.
• The nil value is written as ().
• The nil value can also be written null, for compatibility with JSON; the use of null should be restricted to JSON-related contexts.
• Any function that ends without a return statement implicitly returns nil.
• To declare the value of any type T as nil : T? x = ();

Elvis Operator

• The Elvis Operator is represented by a question mark followed by a colon: ?:

  first operand ?: second operand
  

• If first operand isn't nil, then it will be returned. If it is nil, then the second operand will be returned.

Sample

import ballerina/io;

public function main() {

    int? i = ();
    io:println(i);

    json j = null;
    io:println(j);

    //Elvis Operator
    int k = i ?: 0;
    io:println(k);
}

Output

0