Specify array as a tuple

Question

For instance, I have an abstract class:

type Tuple = [string, number]

abstract class SomeAbstractClass {
    tuples: Tuple[]
}

But when I want to implement this class

class SomeConcreteClass implements SomeAbstractClass {
    public tuples = [
        ['hello', 3],
        ['world', 4]
    ]
}

I am getting an error '(string | number)[][] is not assignable to Tuple[]'. How to tell Typescript that the array I provided actually satisfies the interface?

Give each array a type? public tuples = [ <Tuple>['hello', 3], <Tuple>['world', 4] ]; — Heretic Monkey
– Heretic Monkey, Commented Aug 5, 2021 at 12:14
Maybe it will work out, but it's a coercion, and Typescript suggests to convert it to 'unknown' first. This is a massive construction and I'd like to avoid that. — stahlhammer
– stahlhammer, Commented Aug 5, 2021 at 12:18

captain-yossarian from Ukraine · Accepted Answer · 2021-08-05 12:37:59Z

2

Just use explicit type:

type Tuple = [string, number]

abstract class SomeAbstractClass {
    tuples: Tuple[] = null as any
}

class SomeConcreteClass implements SomeAbstractClass {
    public tuples: Tuple[] = [
        ['hello', 3],
        ['world', 4]
    ]
}

SomeConcreteClass tuples property is mutable, hence TypeScript is unsure whehter it is assignable to abstract class tuples or not

answered Aug 5, 2021 at 12:37

captain-yossarian from Ukraine

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