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  • Flags enums

Flags enums

# Hydroper (5 years ago)

Flags enums would be primitive classes with constants (name:String, value:Number). It'd be very, very efficient.

Of course it's easy to use POJOs ({}) instead of numeric values, but this feature would only provide performance advantages.

The following program implies:

  • String(E.FNX) == 'fnx'
  • E.FNX.valueOf() == 1
  • String(E.QWL_QWERTY) == 'xxxQwerty'
  • E.QWL_QWERTY.valueOf() == 32
  • String(E.WOW_K) == 'wowK'
  • E.WOW_K.valueOf() == 64
enum E {
    FNX,
    QWL_QWERTY = ['xxxQwerty', 32];
    WOW_K;

    f() {
        // Some method
    }
}

var e = E('xxxQwerty');

// constant in e
// E.prototype.set()
// E.prototype.exclude()
// E.prototype.toggle()
// E.prototype.filter()

console.log( 'xxxQwerty' in e );
console.log( ['fnx', 'xxxQwerty'] in e );
console.log( e.set('fnx').exclude('fnx').filter(['fnx', 'xxxQwerty']) );
console.log( e.toggle('xxxQwerty') );
console.log( e.valueOf() );

console.log( E(['fnx', 'xxxQwerty']) );

In typed languages, Array and String would implicitly convert to E.

One could define constant either by omitting expression, by an array literal ([name, value] or [value, name]), by a string literal or by a numeric literal. More examples:

enum E {
    AA_AA;
    LNK = 'vVvVvV';
    QO = 32;
}
# Hydroper (5 years ago)

The com.siteblade.util package contains an approximation of this in ECMAScript.

www.npmjs.com/package/com.siteblade.util

You can use either FlagsEnum or Enum.

import { Enum } from 'com.siteblade.util';

const CollisionType = Enum('CollisionType', [ ['CIRCLE'], ['CUBIC_BEZIER_CURVE', [10]], ['RIGID_BODY', ['rigidBody', 2]] ]);

var type = CollisionType('cubicBezierCurve'); console.log( type == 'cubicBezierCurve' );

valueOf() in this case will return String. If you need number, use the 'number' property.

# Matheus Dias de Souza (5 years ago)

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# Jacob Bloom (5 years ago)

For what it's worth, TypeScript has Enums built-in and I find myself using string literal types instead:

type CollisionType = 'CIRCLE' | 'CUBIC_BEZIER_CURVE' | 'RIGID_BODY';

function handleCollision(type: CollisionType) {
  if (type === 'CIRCLE') {
    // ...
  } else if (type === 'SQUARE') { // Tooling errors on this line
    // ...
  }
}

In VSCode (and I assume other IDEs that support TypeScript) you can even do this in vanilla JS with structured JSDoc comments and the tooling will type check for you:

// @ts-check

/** @typedef {'CIRCLE' | 'CUBIC_BEZIER_CURVE' | 'RIGID_BODY'} CollisionType
*/

/**
 * @param {CollisionType} type
*/
function handleCollision(type) {
  if (type === 'CIRCLE') {
    // ...
  } else if (type === 'SQUARE') { // Tooling errors on this line
    // ...
  }
}

As far as I know, comparing strings is nearly as performant in most JS engines as comparing numbers or objects because they use a method called "string interning"

# Matheus Dias de Souza (5 years ago)

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