Type Alias IsFixedLengthList<T>

IsFixedLengthList: number extends T["length"] ? false : true

Checks if a given readonly array type T has a fixed length (i.e., is a tuple). Returns true if T is a tuple, false if it's a regular array (Type[]).

It works by checking if the general number type is assignable to the specific length property of T. For tuples, T['length'] is a specific number literal (e.g., 3), and number is not assignable to 3. For regular arrays, T['length'] is number, and number is assignable to number.

Type Parameters

T extends readonly unknown[]
The readonly array or tuple type to check.

Returns

true if T is a tuple (fixed length), false otherwise.

Example

type IsTuple = IsFixedLengthList<[1, 2, 3]>; // true
type IsArray = IsFixedLengthList<number[]>; // false
type IsReadonlyArray = IsFixedLengthList<readonly string[]>; // false
type IsEmptyTuple = IsFixedLengthList<[]>; // true
type IsTupleWithRest = IsFixedLengthList<[number, ...string[]]>; // false

Type Alias IsFixedLengthList<T>

Type Parameters

Returns

Example

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