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authorFlorian Dold <florian.dold@gmail.com>2019-12-14 17:55:31 +0100
committerFlorian Dold <florian.dold@gmail.com>2019-12-14 17:55:31 +0100
commit60d154c36bbd6773bbed44da82b17f211604c4b4 (patch)
treee4be6f7e16a19c7e0e18acc7da6e94161742395e
parent749b96284ae0a7e6d03034806deab998a36b7cf6 (diff)
union codecs, error messages
-rw-r--r--src/util/codec-test.ts47
-rw-r--r--src/util/codec.ts72
2 files changed, 113 insertions, 6 deletions
diff --git a/src/util/codec-test.ts b/src/util/codec-test.ts
index d7edd545f..0d1ab5603 100644
--- a/src/util/codec-test.ts
+++ b/src/util/codec-test.ts
@@ -19,14 +19,34 @@
*/
import test from "ava";
-import { stringCodec, objectCodec } from "./codec";
+import {
+ stringCodec,
+ objectCodec,
+ unionCodec,
+ Codec,
+ stringConstCodec,
+} from "./codec";
interface MyObj {
foo: string;
}
-test("basic codec", (t) => {
- const myObjCodec = objectCodec<MyObj>().property("foo", stringCodec).build("MyObj");
+interface AltOne {
+ type: "one";
+ foo: string;
+}
+
+interface AltTwo {
+ type: "two";
+ bar: string;
+}
+
+type MyUnion = AltOne | AltTwo;
+
+test("basic codec", t => {
+ const myObjCodec = objectCodec<MyObj>()
+ .property("foo", stringCodec)
+ .build<MyObj>("MyObj");
const res = myObjCodec.decode({ foo: "hello" });
t.assert(res.foo === "hello");
@@ -34,3 +54,24 @@ test("basic codec", (t) => {
const res2 = myObjCodec.decode({ foo: 123 });
});
});
+
+test("union", t => {
+ const altOneCodec: Codec<AltOne> = objectCodec<AltOne>()
+ .property("type", stringConstCodec("one"))
+ .property("foo", stringCodec)
+ .build("AltOne");
+ const altTwoCodec: Codec<AltTwo> = objectCodec<AltTwo>()
+ .property("type", stringConstCodec("two"))
+ .property("bar", stringCodec)
+ .build("AltTwo");
+ const myUnionCodec: Codec<MyUnion> = unionCodec<MyUnion, "type">("type")
+ .alternative("one", altOneCodec)
+ .alternative("two", altTwoCodec)
+ .build<MyUnion>("MyUnion");
+
+ const res = myUnionCodec.decode({ type: "one", foo: "bla" });
+ t.is(res.type, "one");
+ if (res.type == "one") {
+ t.is(res.foo, "bla");
+ }
+});
diff --git a/src/util/codec.ts b/src/util/codec.ts
index 690486b7d..78516183c 100644
--- a/src/util/codec.ts
+++ b/src/util/codec.ts
@@ -69,6 +69,11 @@ interface Prop {
codec: Codec<any>;
}
+interface Alternative {
+ tagValue: any;
+ codec: Codec<any>;
+}
+
class ObjectCodecBuilder<T, TC> {
private propList: Prop[] = [];
@@ -89,10 +94,10 @@ class ObjectCodecBuilder<T, TC> {
* @param objectDisplayName name of the object that this codec operates on,
* used in error messages.
*/
- build(objectDisplayName: string): Codec<TC> {
+ build<R extends (TC & T)>(objectDisplayName: string): Codec<R> {
const propList = this.propList;
return {
- decode(x: any, c?: Context): TC {
+ decode(x: any, c?: Context): R {
if (!c) {
c = {
path: [`(${objectDisplayName})`],
@@ -107,12 +112,53 @@ class ObjectCodecBuilder<T, TC> {
);
obj[prop.name] = propVal;
}
- return obj as TC;
+ return obj as R;
},
};
}
}
+class UnionCodecBuilder<T, D extends keyof T, TC> {
+ private alternatives = new Map<any, Alternative>();
+
+ constructor(private discriminator: D) {}
+
+ /**
+ * Define a property for the object.
+ */
+ alternative<V>(
+ tagValue: T[D],
+ codec: Codec<V>,
+ ): UnionCodecBuilder<T, D, TC | V> {
+ this.alternatives.set(tagValue, { codec, tagValue });
+ return this as any;
+ }
+
+ /**
+ * Return the built codec.
+ *
+ * @param objectDisplayName name of the object that this codec operates on,
+ * used in error messages.
+ */
+ build<R extends TC>(objectDisplayName: string): Codec<R> {
+ const alternatives = this.alternatives;
+ const discriminator = this.discriminator;
+ return {
+ decode(x: any, c?: Context): R {
+ const d = x[discriminator];
+ if (d === undefined) {
+ throw new DecodingError(`expected tag for ${objectDisplayName} at ${renderContext(c)}.${discriminator}`);
+ }
+ const alt = alternatives.get(d);
+ if (!alt) {
+ throw new DecodingError(`unknown tag for ${objectDisplayName} ${d} at ${renderContext(c)}.${discriminator}`);
+ }
+ return alt.codec.decode(x);
+ }
+ };
+ }
+}
+
/**
* Return a codec for a value that must be a string.
*/
@@ -126,6 +172,20 @@ export const stringCodec: Codec<string> = {
};
/**
+ * Return a codec for a value that must be a string.
+ */
+export function stringConstCodec<V extends string>(s: V): Codec<V> {
+ return {
+ decode(x: any, c?: Context): V {
+ if (x === s) {
+ return x;
+ }
+ throw new DecodingError(`expected string constant "${s}" at ${renderContext(c)}`);
+ }
+ }
+};
+
+/**
* Return a codec for a value that must be a number.
*/
export const numberCodec: Codec<number> = {
@@ -179,3 +239,9 @@ export function mapCodec<T>(innerCodec: Codec<T>): Codec<{ [x: string]: T }> {
export function objectCodec<T>(): ObjectCodecBuilder<T, {}> {
return new ObjectCodecBuilder<T, {}>();
}
+
+export function unionCodec<T, D extends keyof T>(
+ discriminator: D,
+): UnionCodecBuilder<T, D, never> {
+ return new UnionCodecBuilder<T, D, never>(discriminator);
+}