@geronimus/option

Option

Contains functions to create Some and None objects, which you can return from function calls that may or may not return a result.

The idea is to avoid returning null or undefined - whether intentionally, accidentally, or by default - and to make explicit the idea that giving no result is a legitimate possibility, which any code that calls the function must be prepared to deal with.

When the invocation should return a result, you can "wrap" it in a Some.

When there is no result, you return the None singleton object.

Both objects share this common interface:

Properties

isEmpty boolean

true if this is the None object, or a Some object that holds the value undefined or null. false if it is a Some object that holds a value.

Methods

map( transformation ) function

If called on the None object, this method always returns None, no matter what function you pass to it.

If called on a Some object, this method returns another Some object containing the result of applying the transformation function to the original Some's value.

None

None is not a function. It is a singleton object that you may return instead of a call to Some. (Some is a function.)

The None object adheres to to the Option interface described above.

As a simple object, None is not an instanceof anything. You cannot use the new keyword with None, nor does it have any meaning to call None with parentheses.

There is only one None object. As such, None === None returns true.

Some( value )

Creates an instance of a Some object.

The returned object adheres to to the Option interface described above and contains the additional property value, which references the value that the Some object holds.

You can use the keyword new to create a new Some instance, but you do not have to.

Parameters

value any

The value that you want to wrap in a Some object.

Examples

const { None, Some } = require( "@geronimus/option" );

function getFirstItem( array ) {

  if ( !Array.isArray( array ) || array.length === 0 )
    return None;
  else
    return Some( array[ 0 ] );
}

Notes

• If you forget to provide an argument to Some, it will contain the value undefined, which seems like a contradiction. In this case, its isEmpty value will be true. We leave this possibility open ( - rather than, say, returning None when a value is not provided - ) in order not to be too opinionated about its usage.
• These objects provide a (much) simplified implementation of a pattern popularized by the Scala programming language.