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authorPiotr Monwid-Olechnowicz <hasparus@gmail.com>2019-07-03 23:15:10 +0200
committerGitHub <noreply@github.com>2019-07-03 23:15:10 +0200
commit96b65fb40d84ce97b6ca7b814e210a61bca294df (patch)
tree1e12b6440b0d18f902ec27f97eaac0eb08ea788f
parent84cb0e88995b6d2f04a119cc25a695a33e1cbf9f (diff)
[typescript/en] Add tagged union types
They're super useful. https://www.typescriptlang.org/docs/handbook/advanced-types.html#discriminated-unions https://mariusschulz.com/blog/typescript-2-0-tagged-union-types
-rw-r--r--typescript.html.markdown13
1 files changed, 13 insertions, 0 deletions
diff --git a/typescript.html.markdown b/typescript.html.markdown
index 55d8cefe..293a4a35 100644
--- a/typescript.html.markdown
+++ b/typescript.html.markdown
@@ -224,6 +224,19 @@ moreNumbers.push(5); // Error, no push method (because it mutates array)
moreNumbers.length = 3; // Error, length is read-only
numbers = moreNumbers; // Error, mutating methods are missing
+// Tagged Union Types for modelling state that can be in one of many shapes
+type State =
+ | { type: "loading" }
+ | { type: "success", value: number }
+ | { type: "error", message: string };
+
+declare const state: State;
+if (state.type === "success") {
+ console.log(state.value);
+} else if (state.type === "error") {
+ console.error(state.message);
+}
+
// Iterators and Generators
// for..of statement