feat(types): IsFunction, IfFunction

Signed-off-by: Lexus Drumgold <[email protected]>

.eslintrc.cjs

@@ -16,6 +16,7 @@ const config = {
       files: [
         'src/types/built-in.ts',
         'src/types/exact-optional-property-types.ts',
+        'src/types/fn.ts',
         'src/types/overwrite.ts'
       ],
       rules: {

src/types/__tests__/if-function.spec-d.ts

@@ -0,0 +1,20 @@
+/**
+ * @file Type Tests - IfFunction
+ * @module tutils/types/tests/unit-d/IfFunction
+ */
+
+import type Fn from '../fn'
+import type TestSubject from '../if-function'
+
+describe('unit-d:types/IfFunction', () => {
+  type False = false
+  type True = true
+
+  it('should equal False if IsFunction<T> extends false', () => {
+    expectTypeOf<TestSubject<Fn[], True, False>>().toEqualTypeOf<False>()
+  })
+
+  it('should equal True if IsFunction<T> extends true', () => {
+    expectTypeOf<TestSubject<Fn, True, False>>().toEqualTypeOf<True>()
+  })
+})

src/types/__tests__/is-function.spec-d.ts

@@ -0,0 +1,17 @@
+/**
+ * @file Type Tests - IsFunction
+ * @module tutils/types/tests/unit-d/IsFunction
+ */
+
+import type Fn from '../fn'
+import type TestSubject from '../is-function'
+
+describe('unit-d:types/IsFunction', () => {
+  it('should equal false if T does not extend Fn', () => {
+    expectTypeOf<TestSubject<Date>>().toEqualTypeOf<false>()
+  })
+
+  it('should equal true if T extends Fn', () => {
+    expectTypeOf<TestSubject<Fn>>().toEqualTypeOf<true>()
+  })
+})

src/types/fn.ts

@@ -9,6 +9,6 @@
  * @template A - Arguments type
  * @template R - Return type
  */
-type Fn<A extends any[] = any[], R = any> = (...args: A) => R
+type Fn<A extends any[] = any[], R = any> = Function & ((...args: A) => R)
 
 export type { Fn as default }

src/types/if-function.ts

@@ -0,0 +1,20 @@
+/**
+ * @file Type Definitions - IfFunction
+ * @module tutils/types/IfFunction
+ */
+
+import type IsFunction from './is-function'
+
+/**
+ * Conditional type that resolves depending on whether or not `T` extends
+ * `Fn`.
+ *
+ * @see {@linkcode IsFunction}
+ *
+ * @template T - Type to evaluate
+ * @template True - Type if `T` extends `Fn`
+ * @template False - Type if `T` does not extend `Fn`
+ */
+type IfFunction<T, True, False> = IsFunction<T> extends true ? True : False
+
+export type { IfFunction as default }

src/types/index.ts

@@ -26,11 +26,13 @@ export type { default as IfAny } from './if-any'
 export type { default as IfArray } from './if-array'
 export type { default as IfBigInt } from './if-big-int'
 export type { default as IfBoolean } from './if-boolean'
+export type { default as IfFunction } from './if-function'
 export type { default as IndexSignature } from './index-signature'
 export type { default as IsAny } from './is-any'
 export type { default as IsArray } from './is-array'
 export type { default as IsBigInt } from './is-big-int'
 export type { default as IsBoolean } from './is-boolean'
+export type { default as IsFunction } from './is-function'
 export type { default as IsTuple } from './is-tuple'
 export type { default as Join } from './join'
 export type { default as JsonArray } from './json-array'

src/types/is-function.ts

@@ -0,0 +1,15 @@
+/**
+ * @file Type Definitions - IsFunction
+ * @module tutils/types/IsFunction
+ */
+
+import type Fn from './fn'
+
+/**
+ * Returns a boolean indicating if `T` extends {@linkcode Fn}.
+ *
+ * @template T - Type to evaluate
+ */
+type IsFunction<T> = T extends Fn ? true : false
+
+export type { IsFunction as default }