A discriminated union (also known as tagged unions or algebraic data types) is an advanced pattern that combines string literal types, union types, type guards, and types aliases.
Discriminated unions use a type guard to narrow union types based on tests of a discriminant property (a string literal type) and furthermore extend that capability to switch statements.
The following code snippet declares three types that share a string literal property named kind:
interface Cube { kind: "cube"; size: number;}interface Pyramid { kind: "pyramid"; width: number; length: number; height: number;}interface Sphere { kind: "sphere"; radius: number;}
We then declare the union type of the three types declared in the preceding code snippet: ...
