TS: Vector3 interface not descriptive enough to support this valid usage

Description of the problem

The following code works, but TypeScript does not compile with the present Vector3.d.ts

  // vector between center of head and center of ear
  const earVector = new THREE.Vector3(1.44, 0.6, -0.3);

  const leftEar = new THREE.SphereGeometry(1, 32, 32).applyMatrix4(new THREE.Matrix4().makeScale(0.4, 0.4, 0.25));
  const rightEar = leftEar.clone();

  leftEar.translate(...earVector.toArray());
  earVector.x = -earVector.x;
  rightEar.translate(...earVector.toArray());

BUG (compile error): Expected 3 arguments, but got 0 or more. ts(2556)

EXPECTED: Given that the code behaves as expected, I would expect it to compile. (I would also expect the aesthetics of this use of the spread operator to divide opinion)

Three.js version

• Dev
• r116
• …

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• All of them
• Windows
• macOS
• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, …)

N/A

[donmccurdy]

I’ve used this syntax elsewhere:

export type vec2 = [number, number];

export type vec3 = [number, number, number];

export type vec4 = [number, number, number, number];

export type mat3 = [
	number, number, number,
	number, number, number,
	number, number, number,
];

export type mat4 = [
	number, number, number, number,
	number, number, number, number,
	number, number, number, number,
	number, number, number, number,
];

There is no list/tuple distinction at runtime, this is just for typechecking.

[gkjohnson]

From this stackoverflow answer it sounds like you could define fixed array types of a specific length and reuse them but I haven’t tested it:

// ReusableTypes.d.ts
export type Length3Array = [ number, number, number ];
export type Length4Array = [ number, number, number, number ];
export type Length16Array = [ /* ... */ ];

// Vector3.d.ts
class Vector3 {

    // ...

    toArray() : Length3Array;

}