v0.44.0

Minor Changes

• d2c28aa: feat: adds has module

  • has.oneProperty lets you express a constraint that the input type contains exactly 1 property. For example:

    /**
     * @example
     *  const one = singleton({ a: 1 })       // ✅
    
     *  const zero = singleton({})            // 🚫
     *  //    ^? const zero: never
     *  const two = singleton({ a: 1, b: 2 }) // 🚫
     *  //    ^? const two: never
     */
    declare function singleton<const T extends has.oneProperty<T>>(
      objectWithExactlyOneProperty: T
    ): T;

    Note: has.oneProperty accepts 2 additional optional type parameters

    1. an invariant, which allows you to apply an additional constraint on the type of the property itself; and
    2. a "debug" flag, which, if non-never, changes the behavior of has.oneProperty to raise a custom TypeError if T fails to satisfy the constraint

  • has.oneElement

    /**
     * @example
     *  const one = singleton([1])    // ✅
     *  //    ^? const one: readonly [1]
     *
     *  const zero = singleton([])    // 🚫
     *  //    ^? const zero: never
     *  const two = singleton([1, 2]) // 🚫
     *  //    ^? const two: never
     */
    declare function oneNumber<const T extends has.oneElement<T, number>>(
      tupleContainingOneNumber: T
    ): T;

    Note: like has.oneProperty, has.oneElement also accepts 2 additional optional type parameters

    1. an invariant, which allows you to apply an additional constraint on the type of the element itself; and,
    2. a "debug" flag, which, if non-never, changes the behavior of has.oneElement to raise a custom TypeError if T fails to satisfy the constraint