feat: add $.spread (#58)

add $.spread

fixtures.rs

@@ -36,6 +36,9 @@ pub mod object_fixtures;
 #[path = "./result/fixtures.rs"]
 pub mod result_fixtures;
 
+#[path = "./spread/fixtures.rs"]
+pub mod spread_fixtures;
+
 #[path = "./str/fixtures.rs"]
 pub mod str_fixtures;
 

mod.ts

@@ -13,6 +13,7 @@ export * from "./object/codec.ts";
 export * from "./option/codec.ts";
 export * from "./option/optionBool/codec.ts";
 export * from "./result/codec.ts";
+export * from "./spread/codec.ts";
 export * from "./str/codec.ts";
 export * from "./transform/codec.ts";
 export * from "./tuple/codec.ts";

spread/__snapshots__/test.ts.snap

@@ -0,0 +1,12 @@
+export const snapshot = {};
+
+snapshot[`object { _tag: "a", bar: 123 } 1`] = `
+00
+7b
+`;
+
+snapshot[`object { _tag: "b", x: 0, bar: 123 } 1`] = `
+01
+00
+7b
+`;

spread/codec.ts

@@ -0,0 +1,14 @@
+import { Codec, createCodec } from "../common.ts";
+
+export function spread<A, B>($a: Codec<A>, $b: Codec<B>) {
+  return createCodec<A & B>({
+    _staticSize: $a._staticSize + $b._staticSize,
+    _encode(buffer, value) {
+      $a._encode(buffer, value);
+      $b._encode(buffer, value);
+    },
+    _decode(buffer) {
+      return { ...$a._decode(buffer), ...$b._decode(buffer) };
+    },
+  });
+}

spread/fixtures.rs

@@ -0,0 +1,19 @@
+use parity_scale_codec::Encode;
+
+#[derive(Encode)]
+enum Foo {
+  A,
+  B(u8),
+}
+
+#[derive(Encode)]
+struct Bar(u8);
+
+#[derive(Encode)]
+struct Foobar(Foo, Bar);
+
+#[rustfmt::skip]
+crate::fixtures!(
+  Foobar(Foo::A, Bar(123)),
+  Foobar(Foo::B(0), Bar(123)),
+);

spread/test.ts

@@ -0,0 +1,17 @@
+import * as $ from "../mod.ts";
+import { testCodec } from "../test-util.ts";
+
+const $foo = $.taggedUnion(
+  "_tag",
+  ["a"],
+  ["b", ["x", $.u8]],
+);
+
+const $bar = $.object(["bar", $.u8]);
+
+const $foobar = $.spread($foo, $bar);
+
+testCodec("object", $foobar, [
+  { _tag: "a", bar: 123 },
+  { _tag: "b", x: 0, bar: 123 },
+]);