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I am having problems while overloading constructors, it won't let me tell it what type is what the variable contains. How can I force a type, or make this work anyway...?

constructor(points: Point[], name?: string); constructor(walls: Wall[], name?: string); constructor(pointsOrWalls: (Wall | Point)[], name?: string) { if (pointsOrWalls[0] instanceof Point) { // If first is Point all must be Points // But here typescript says that pointsOrWalls is of type (Wall | Point)[] this.walls = pointsOrWalls.map(function(point, ind, points) { return new Wall(point, points[++ind % points.length]) }) }else{ // Since these aren't points they are Walls this.walls = walls } this.name = name }
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How can I force a type, or make this work anyway...

Use a type assertion: 

// If first is Point all must be Points let points = pointsOrWalls as Point[];

Complete: 

class Wall {w} class Point {p} class Foo { walls; name constructor(points: Point[], name?: string); constructor(walls: Wall[], name?: string); constructor(pointsOrWalls: (Wall | Point)[], name?: string) { if (pointsOrWalls[0] instanceof Point) { // If first is Point all must be Points let points = pointsOrWalls as Point[]; // But here typescript says that pointsOrWalls is of type (Wall | Point)[] this.walls = points.map(function(point, ind, points) { return new Wall(point, points[++ind % points.length]) }) }else{ // Since these aren't points they are Walls this.walls = walls } this.name = name } }

More

https://basarat.gitbooks.io/typescript/content/docs/types/type-assertion.html

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5 Comments

Although this is good, is there any way to not re-declare variable?
You can create a user defined type guard
Don't understand, what guard?
@Akxe I just wrote docs for your : basarat.gitbooks.io/typescript/content/docs/types/… 🌹
Thank you so much, this is definitely worth being in bookmarks

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