Class MatchBuilder<T, R, HasInput, Handled, Locked>

Fluent builder for match. Tracks the handled cases at the type level so .exhaustive() only compiles when every union member is covered.

The Locked phantom flag (set via .returnType<R>()) constrains every subsequent handler to return R, useful when branch return-type inference would widen to a union narrower than the target slot (e.g. ReactNode, an API DTO).

Example

const describe = match<Event>()
  .with({ kind: "click" }, (e) => `click @ ${e.x},${e.y}`)
  .with({ kind: "key" },   (e) => `key ${e.code}`)
  .exhaustive();

Type Parameters

T
R = never
HasInput extends boolean = false
Handled extends readonly unknown[] = []
Locked extends boolean = false

Index

Constructors

constructor

new MatchBuilder<
    T,
    R = never,
    HasInput extends boolean = false,
    Handled extends readonly unknown[] = [],
    Locked extends boolean = false,
>(
    cases?: readonly Case<T, unknown>[],
    input?: T,
    _handled?: Handled,
): MatchBuilder<T, R, HasInput, Handled, Locked>
Type Parameters
- T
- R = never
- HasInput extends boolean = false
- Handled extends readonly unknown[] = []
- Locked extends boolean = false
Parameters
- cases: readonly Case<T, unknown>[] = []
- Optionalinput: T
- _handled: Handled = ...
Returns MatchBuilder<T, R, HasInput, Handled, Locked>
- Defined in match.ts:117

Properties

`Readonly`_handled

_handled: Handled = ...

Methods

exhaustive

exhaustive(): ExhaustiveResult<T, Handled, R, HasInput>
Returns ExhaustiveResult<T, Handled, R, HasInput>
- Defined in match.ts:197

otherwise

otherwise(handler: (input: T) => R): HasInput extends true ? R : (input: T) => R
Parameters
- handler: (input: T) => R
Returns HasInput extends true ? R : (input: T) => R
- Defined in match.ts:204

returnType

returnType<R2>(): MatchBuilder<T, R2, HasInput, Handled, true>
Lock the result type. All subsequent .with() handlers must return R2. Useful when branch return-type inference widens to a union narrower than the slot the match feeds into (e.g. ReactNode).
Type Parameters
- R2
Returns MatchBuilder<T, R2, HasInput, Handled, true>
- Defined in match.ts:180

run

run(input?: T): R
Run on the value passed to match, or on input when curried.
Parameters
- Optionalinput: T
Returns R
- Defined in match.ts:185

with

with<const P, R2>(
    pattern: P,
    handler: (input: Narrow<T, P>) => HandlerReturn<Locked, R, R2>,
): MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, ExhaustMatched<T, P>],
    Locked,
>
Type Parameters
- const P
- R2
Parameters
- pattern: P
- handler: (input: Narrow<T, P>) => HandlerReturn<Locked, R, R2>
Returns MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, ExhaustMatched<T, P>],
    Locked,
>
- Defined in match.ts:124

withEither

withEither<const P1, const P2, R2>(
    pattern1: P1,
    pattern2: P2,
    handler: (
        input: NarrowUnion<T, readonly [P1, P2]>,
    ) => HandlerReturn<Locked, R, R2>,
): MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, NarrowUnion<T, readonly [P1, P2]>],
    Locked,
>
withOneOf for exactly two patterns.
Type Parameters
- const P1
- const P2
- R2
Parameters
- pattern1: P1
- pattern2: P2
- handler: (input: NarrowUnion<T, readonly [P1, P2]>) => HandlerReturn<Locked, R, R2>
Returns MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, NarrowUnion<T, readonly [P1, P2]>],
    Locked,
>
- Defined in match.ts:161

withOneOf

withOneOf<const Ps extends readonly Pattern<T>[], R2>(
    patterns: Ps,
    handler: (input: NarrowUnion<T, Ps>) => HandlerReturn<Locked, R, R2>,
): MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, NarrowUnion<T, Ps>],
    Locked,
>
One handler for several patterns (OR). Handler input is the union of narrowed members.
Type Parameters
- const Ps extends readonly Pattern<T>[]
- R2
Parameters
- patterns: Ps
- handler: (input: NarrowUnion<T, Ps>) => HandlerReturn<Locked, R, R2>
Returns MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, NarrowUnion<T, Ps>],
    Locked,
>
- Defined in match.ts:144

Class MatchBuilder<T, R, HasInput, Handled, Locked>

Example

Type Parameters

Index

Constructors

Properties

Methods

Constructors

constructor

Type Parameters

Parameters

Returns MatchBuilder<T, R, HasInput, Handled, Locked>

Properties

`Readonly`_handled

Methods

exhaustive

Returns ExhaustiveResult<T, Handled, R, HasInput>

otherwise

Parameters

Returns HasInput extends true ? R : (input: T) => R

returnType

Type Parameters

Returns MatchBuilder<T, R2, HasInput, Handled, true>

run

Parameters

Returns R

with

Type Parameters

Parameters

Returns MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, ExhaustMatched<T, P>],
    Locked,
>

withEither

Type Parameters

Parameters

Returns MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, NarrowUnion<T, readonly [P1, P2]>],
    Locked,
>

withOneOf

Type Parameters

Parameters

Returns MatchBuilder<
    T,
    NextResult<Locked, R, R2>,
    HasInput,
    readonly [Handled, NarrowUnion<T, Ps>],
    Locked,
>

Settings

On This Page

Class MatchBuilder<T, R, HasInput, Handled, Locked>

Example

Type Parameters

Index

Constructors

Properties

Methods

Constructors

constructor

Type Parameters

Parameters

Returns MatchBuilder<T, R, HasInput, Handled, Locked>

Properties

Readonly_handled

Methods

exhaustive

Returns ExhaustiveResult<T, Handled, R, HasInput>

otherwise

Parameters

Returns HasInput extends true ? R : (input: T) => R

returnType

Type Parameters

Returns MatchBuilder<T, R2, HasInput, Handled, true>

run

Parameters

Returns R

with

Type Parameters

Parameters

Returns MatchBuilder< T, NextResult<Locked, R, R2>, HasInput, readonly [Handled, ExhaustMatched<T, P>], Locked,>

withEither

Type Parameters

Parameters

Returns MatchBuilder< T, NextResult<Locked, R, R2>, HasInput, readonly [Handled, NarrowUnion<T, readonly [P1, P2]>], Locked,>

withOneOf

Type Parameters

Parameters

Returns MatchBuilder< T, NextResult<Locked, R, R2>, HasInput, readonly [Handled, NarrowUnion<T, Ps>], Locked,>

Settings

On This Page

`Readonly`_handled

Returns MatchBuilder<
T,
NextResult<Locked, R, R2>,
HasInput,
readonly [Handled, ExhaustMatched<T, P>],
Locked,
>

Returns MatchBuilder<
T,
NextResult<Locked, R, R2>,
HasInput,
readonly [Handled, NarrowUnion<T, readonly [P1, P2]>],
Locked,
>

Returns MatchBuilder<
T,
NextResult<Locked, R, R2>,
HasInput,
readonly [Handled, NarrowUnion<T, Ps>],
Locked,
>