Updating defaultTo type definitions

test/defaultTo.test.ts

@@ -0,0 +1,49 @@
+import { expectType } from 'tsd';
+import { defaultTo, __ } from '../es';
+
+expectType<'fallback'>(defaultTo('fallback', undefined));
+expectType<'fallback'>(defaultTo('fallback', null));
+expectType<string>(defaultTo('fallback')(undefined));
+expectType<string>(defaultTo('fallback')(null));
+expectType<'fallback'>(defaultTo(__, undefined)('fallback'));
+expectType<'fallback'>(defaultTo(__, null)('fallback'));
+
+expectType<'string value'>(defaultTo('fallback', 'string value'));
+expectType<'string value'>(defaultTo('fallback')('string value'));
+
+expectType<0>(defaultTo(0, undefined));
+expectType<0>(defaultTo(0, null));
+expectType<number>(defaultTo(0)(undefined));
+expectType<number>(defaultTo(0)(null));
+expectType<0>(defaultTo(__, undefined)(0));
+expectType<0>(defaultTo(__, null)(0));
+
+expectType<2>(defaultTo(0, 2));
+expectType<2>(defaultTo(0)(2));
+expectType<number>(defaultTo(__, 2)(0));
+
+expectType<'two'>(defaultTo(0, 'two'));
+expectType<'two'>(defaultTo(0)('two'));
+expectType<string>(defaultTo(__, 'two')(0));
+expectType<2>(defaultTo('zero', 2));
+expectType<2>(defaultTo('zero')(2));
+expectType<number>(defaultTo(__, 2)('zero'));
+
+const stringOrUndefined = Math.random() < 0.5 ? Math.random().toString(32) : undefined;
+expectType<0 | string>(defaultTo(0, stringOrUndefined));
+expectType<number | string>(defaultTo(0)(stringOrUndefined));
+expectType<0 | string>(defaultTo(__, stringOrUndefined)(0));
+const stringOrNull = Math.random() < 0.5 ? Math.random().toString(32) : null;
+expectType<0 | string>(defaultTo(0, stringOrNull));
+expectType<number | string>(defaultTo(0)(stringOrNull));
+expectType<0 | string>(defaultTo(__, stringOrNull)(0));
+
+
+const numberOrUndefined = Math.random() < 0.5 ? Math.random() : undefined;
+expectType<'fallback' | number>(defaultTo('fallback', numberOrUndefined));
+expectType<string | number>(defaultTo('fallback')(numberOrUndefined));
+expectType<'fallback' | number>(defaultTo(__, numberOrUndefined)('fallback'));
+const numberOrNull = Math.random() < 0.5 ? Math.random() : null;
+expectType<'fallback' | number>(defaultTo('fallback', numberOrNull));
+expectType<string | number>(defaultTo('fallback')(numberOrNull));
+expectType<'fallback' | number>(defaultTo(__, numberOrNull)('fallback'));

types/defaultTo.d.ts

@@ -1,2 +1,5 @@
-export function defaultTo<T, U>(a: T, b: U | null | undefined): T | U;
-export function defaultTo<T>(a: T): <U>(b: U | null | undefined) => T | U;
+import { DefaultTo, Placeholder } from './util/tools';
+
+export function defaultTo<Fallback>(a: Fallback): <Value>(b: Value) => DefaultTo<Fallback, Value>;
+export function defaultTo<Value>(__: Placeholder, b: Value): <Fallback>(a: Fallback) => DefaultTo<Fallback, Value>;
+export function defaultTo<Fallback, Value>(a: Fallback, b: Value): DefaultTo<Fallback, Value>;

types/util/tools.d.ts

@@ -30,6 +30,12 @@ export type CondPair<T extends any[], R> = [(...val: T) => boolean, (...val: T)
  */
 export type CondPairTypeguard<T, TFiltered extends T, R> = [(value: T) => value is TFiltered, (value: TFiltered) => R];
 
+/**
+ * A conditional type to use with default values. (defaultTo, propOr, etc)
+ * <created by @lax4mike>
+ */
+export type DefaultTo<Fallback, Value> = (Value extends (null | undefined) ? Fallback | Exclude<Value, null | undefined> : Value);
+
 /**
  * Represents all objects evolvable with Evolver E
  * @param E