I’ve used the following type:

type FixedSizeArray<N extends number, T> = {
  length: N
} & ReadonlyArray<T>

But then TS doesn’t accept

someProp: Array.from({ length: 16 }).map(() => '')

where someProp expects FixedSizeArray<16, string>.

I either have to cast it or write '' 16 times. The actual error thrown being:

Type 'string[]' is not assignable to type 'FixedSizeArray<16, string>'.
  Type 'string[]' is not assignable to type '{ length: 16; }'.
    Types of property 'length' are incompatible.
      Type 'number' is not assignable to type '16'.ts(2322)

See this answer for implementation details.

Is this a TS bug or am I doing something wrong?