Proposal: Static constructors

[nin-jin]

Example:

class Component {
    static all : Array<typeof Component>
    static constructor() {
        Component.all.push( this )
    }
}

class MyButton extends {}
class MyCheckbox extends {}
class MyRadio extends {}

console.assert( Component.all[0] === MyButton , 'registration MyButton' )
console.assert( Component.all[1] === MyCheckbox , 'registration MyChackbox' )
console.assert( Component.all[2] === MyRadio , 'registration MyRadio' )

This not works. But we have workaround:

/// Support for static constructors
var __extends = ( Sub , Sup ) => {
    for( var prop in Sup ) if( Sup.hasOwnProperty( prop ) ) Sub[ prop ] = Sup[ prop ]
    Sub.prototype = Object.create( Sup.prototype )
    Sub.prototype.constructor = Sub
    if( Sub.initializer ) Sub.initializer()
};

class Component {
    static all : Array<typeof Component> = []
    static initializer() {
        Component.all.push( this )
    }
}

class MyButton extends Component {}
class MyCheckbox extends Component {}
class MyRadio extends Component {}

console.assert( Component.all[0] === MyButton , 'registration MyButton' )
console.assert( Component.all[1] === MyCheckbox , 'registration MyChackbox' )
console.assert( Component.all[2] === MyRadio , 'registration MyRadio' )

But:

• This is hack.
• initializer calls only on descendant classes.

We can use decorators:

class Component {
    static all : Array<typeof Component> = []
    static register( comp : typeof Component ) {
        Component.all.push( comp )
    }
}

@ Component.register
class MyButton extends Component {}

@ Component.register
class MyCheckbox extends Component {}

@ Component.register
class MyRadio extends Component {}

console.assert( Component.all[0] === MyButton , 'registration MyButton' )
console.assert( Component.all[1] === MyCheckbox , 'registration MyChackbox' )
console.assert( Component.all[2] === MyRadio , 'registration MyRadio' )

But:

• Too more code.
• User may forget to register component and don't understand why his code not works.

[basarat]

Static constructors have been asked before : #265

Where the pattern was recommended https://basarat.gitbooks.io/typescript/content/docs/tips/staticConstructor.html 🌹

[mhegazy]

indeed a duplicate of #265. closing.

[nin-jin]

@basarat, Dependency on caring user - antipattern. Best practice - automatic enshuring of invariants. Static constructors is minimal feature for that.