whenElse
The whenElse() function offers two explicit branches: if the predicate is true, theFunction runs, otherwise elseFunction. Return types stay disjoint and preserved.
WARNING
Very unstable typing - TypeScript is not very kind with us
Interactive example
Syntax
Classic signatures
typescript
// Type Guard predicate
function whenElse<
GenericInput extends AnyValue,
GenericPredicatedInput extends GenericInput,
GenericOutput1 extends AnyValue | EscapeVoid,
GenericOutput2 extends AnyValue | EscapeVoid
>(
input: GenericInput,
predicate: (input: GenericInput) => input is GenericPredicatedInput,
theFunction: (predicatedInput: GenericPredicatedInput) => GenericOutput1,
elseFunction: (predicatedInput: Exclude<GenericInput, GenericPredicatedInput>) => GenericOutput2
): GenericOutput1 | GenericOutput2;
// Boolean predicate
function whenElse<
GenericInput extends AnyValue,
GenericOutput1 extends AnyValue | EscapeVoid,
GenericOutput2 extends AnyValue | EscapeVoid
>(
input: GenericInput,
predicate: (input: GenericInput) => boolean,
theFunction: (predicatedInput: GenericInput) => GenericOutput1,
elseFunction: (predicatedInput: GenericInput) => GenericOutput2
): BreakGenericLink<GenericOutput1> | BreakGenericLink<GenericOutput2>;Curried signatures
typescript
// Type Guard predicate
function whenElse<
GenericInput extends AnyValue,
GenericPredicatedInput extends GenericInput,
GenericOutput1 extends AnyValue | EscapeVoid,
GenericOutput2 extends AnyValue | EscapeVoid
>(
predicate: (input: GenericInput) => input is GenericPredicatedInput,
theFunction: (predicatedInput: GenericPredicatedInput) => GenericOutput1,
elseFunction: (predicatedInput: Exclude<GenericInput, GenericPredicatedInput>) => GenericOutput2
): (
input: GenericInput
) => BreakGenericLink<GenericOutput1> | BreakGenericLink<GenericOutput2>;
// Boolean predicate
function whenElse<
GenericInput extends AnyValue,
GenericOutput1 extends AnyValue | EscapeVoid,
GenericOutput2 extends AnyValue | EscapeVoid
>(
predicate: (input: GenericInput) => boolean,
theFunction: (predicatedInput: GenericInput) => GenericOutput1,
elseFunction: (predicatedInput: GenericInput) => GenericOutput2
): (
input: GenericInput
) => GenericOutput1 | GenericOutput2;Parameters
input: The value tested (optional in curried mode).predicate: Decision function (can be a type guard).theFunction: Function executed if the predicate is true.elseFunction: Function executed otherwise.
Return value
The result of theFunction or elseFunction depending on the predicate result, with distinct typing.