fix: issue sindresorhus#788 added ifEqual guard

index.d.ts

@@ -99,6 +99,7 @@ export type {IsAny} from './source/is-any';
 export type {IfAny} from './source/if-any';
 export type {IsNever} from './source/is-never';
 export type {IfNever} from './source/if-never';
+export type {IfEqual} from './source/if-equal';
 export type {IsUnknown} from './source/is-unknown';
 export type {IfUnknown} from './source/if-unknown';
 export type {ArrayIndices} from './source/array-indices';

source/if-equal.d.ts

@@ -0,0 +1,24 @@
+import type { IsEqual } from './is-equal';
+
+/**
+ * An if-else-like type that resolves depending on whether the two given types are equal.
+ *
+ * @see {@link IsEqual}
+ *
+ * @example
+ * ```
+ * import type { IfEqual } from 'type-fest';
+ *
+ * type Result1 = IfEqual<string, string, 'Equal', 'NotEqual'>;
+ * //=> 'Equal'
+ *
+ * type Result2 = IfEqual<string, number, 'Equal', 'NotEqual'>;
+ * //=> 'NotEqual'
+ * ```
+ *
+ * @category Type Guard
+ * @category Utilities
+ */
+export type IfEqual<A, B, TypeIfEqual = true, TypeIfNotEqual = false> = (
+ IsEqual<A, B> extends true ? TypeIfEqual : TypeIfNotEqual
+);

test-d/if-equal.ts

@@ -0,0 +1,18 @@
+import { expectType, expectError } from 'tsd';
+import type { IfEqual } from '../index';
+
+// `IfEqual` should return `true`/`false` if only `A` and `B` are specified
+expectType<IfEqual<string, string>>(true);
+expectType<IfEqual<string, number>>(false);
+
+// `IfEqual` with custom types for equal or not equal cases
+expectType<IfEqual<string, string, 'Equal', 'NotEqual'>>('Equal');
+expectType<IfEqual<string, number, 'Equal', 'NotEqual'>>('NotEqual');
+
+// `IfEqual` should correctly handle complex types
+expectType<IfEqual<{ a: number }, { a: number }>>(true);
+expectType<IfEqual<{ a: number }, { b: number }>>(false);
+
+// Missing generic parameters
+expectError<IfEqual<string>>(undefined);
+expectError<IfEqual>(undefined);