Tuple types for Coordinate, Size, Extent, etc.

[janruo]

Currently the array types like Coordinate, Size, Extent are defined as Array<number>. This works for plain Javascript and for Typescript when the noUncheckedIndexedAccess compiler flag is disabled (default).

However, if extra type safety is wanted and the flag is enabled, those types become difficult to use. Typescript can't tell how many values a number array contains, so all extracted values will be number | undefined.

Would it be possible for Openlayers to define these types as tuples instead?

• Extent would be [number, number, number, number]
• Size would be [number, number]
• Coordinate would probably have to be [number, number] | [number, number, number] | [number, number, number, number]

Example:

type CurrentCoordinate = number[];
type BetterCoordinate = [number, number] | [number, number, number] | [number, number, number, number];

const currentCoordinate = [1, 2] as CurrentCoordinate;
const betterCoordinate = [1, 2] as BetterCoordinate;
const betterXyzCoordinate = [1, 2, 3] as BetterCoordinate;

// Error: object is possibly 'undefined' :(
const foo = currentCoordinate[0] + 1;

// Just works :)
const bar = betterCoordinate[0] + 1;

// Any coordinate is guaranteed to have at least the X and Y
// x = number
// y = number
// z = number | undefined
// m = number | undefined
const [x, y, z, m] = betterXyzCoordinate;

[M393]

Here is a previous discussion: #14166