Symbol

A Symbol is a unique opaque value. When a symbol is created no other Symbol value will ever be equal to it.

To create a Symbol you can use the double dollar sign expression $$:

let mySymbol = $$;

let mySymbol2 = $$;

io.print(mySymbol == mySymbol); // true;

io.print(mySymbol == mySymbol2); // false;

io.print($$ == $$); // false;

You can assign a description to the Symbol by passing a String between the $$ expression, this can be useful for debugging purposes:

let mySymbol = $"My Symbol"$;

io.print(mySymbol);

Outputs:

[Symbol "My Symbol"]

note

melon's Symbol values are nothing like Ruby's symbols even though they share the same name. They are inspired by ES6 JavaScript's Symbols.

Usage

Symbols are useful to control the visibility of an Object's property value, see here.