make match infer its return type

Mike96Angelo · Feb 25, 2023 · 5a6c73b · 5a6c73b
1 parent 6d1d285
commit 5a6c73b
Show file tree

Hide file tree

Showing 5 changed files with 14 additions and 13 deletions.
diff --git a/example.ts b/example.ts
@@ -41,7 +41,7 @@ const handleA = (abc: ABC) => {
   }
   console.log(
     abc,
-    abc.match<string | number | boolean>({
+    abc.match({
       A(a) {
         return `A: ${a}`;
       },

diff --git a/optional-pair.ts b/optional-pair.ts
@@ -40,10 +40,10 @@ class OptionalPair<
     });
   }
 
-  both(): Optional<[first: A, second: B]> {
+  both(): Optional<Readonly<[first: A, second: B]>> {
     return this.match({
       Both(first, second) {
-        return toOptional([first, second]);
+        return toOptional([first, second] as const);
       },
       _() {
         return None;

diff --git a/package.json b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "variant-match",
-  "version": "2.0.3",
+  "version": "2.0.4",
   "description": "Brings variant match pattern to TypeScript.",
   "main": "mod.js",
   "scripts": {

diff --git a/result.ts b/result.ts
@@ -149,10 +149,10 @@ class Result<
   ): Result<T, E> {
     return this.match({
       Ok(value) {
-        return filter(value) ? Ok(value) : Err(error());
+        return filter(value) ? Ok<T, E>(value) : Err<T, E>(error());
       },
       Err() {
-        return Err(error());
+        return Err<T, E>(error());
       },
     });
   }

diff --git a/variant.ts b/variant.ts
@@ -11,6 +11,8 @@ type Matcher<V, R> = UnionToIntersection<
   V extends Variant<infer K, any> ? Record<K, VariantBranch<V, R>> : never
 >;
 
+type MatcherReturn<M> = M extends Matcher<any, infer R> ? R : never;
+
 const assertVariant = (v: any) => {
   const hasType = typeof v?.kind === "string";
   const hasValues = Array.isArray(v?.values);
@@ -69,13 +71,12 @@ abstract class VariantTypeClass<V extends Variant<any, any[]>> {
    *                   all branches independently.
    * @returns The result of the named branch or catchAll that was executed.
    */
-  match<R>(matcher: Exact<Matcher<V, R>, V["kind"]>): R;
-  match<R>(
-    matcher: Exact<
-      Partial<Matcher<V, R>> & Record<"_", Func<[this], R>>,
-      V["kind"] | "_"
-    >
-  ): R;
+  match<M extends Matcher<V, any>>(
+    matcher: Exact<M, V["kind"]>
+  ): MatcherReturn<M>;
+  match<M extends Partial<Matcher<V, any>>, R>(
+    matcher: Exact<M & Record<"_", Func<[this], R>>, V["kind"] | "_">
+  ): R | MatcherReturn<M>;
   match(matcher: any) {
     const func = matcher[this.variant.kind] ?? matcher._;