union

union() composes several patterns into a single reusable ToolPattern. Useful for sharing patterns between match, when, isMatch, or anywhere else a pattern is expected.

Interactive example

Syntax

function union<
	GenericInput extends unknown, 
	const GenericPatterns extends readonly [
    	Pattern<GenericInput extends infer InferredInput ? InferredInput : never>,
    	...Pattern<GenericInput extends infer InferredInput ? InferredInput : never>[]
	]
>(
	...patterns: FixDeepFunctionInfer<
		readonly [Pattern<GenericInput>, ...Pattern<GenericInput>[]], 
		GenericPatterns
	>
): ToolPattern<
	GenericInput, 
	GenericPatterns[number] extends infer InferredPattern ? InferredPattern : never
>;

Parameters

• patterns: patterns to combine (literals, partial objects, tuples, predicates, other ToolPattern).

Return value

A ToolPattern that matches if at least one of the provided patterns matches. You can pass it to match, when, isMatch, or compose it in other union.

Best practices

• Group your business patterns (e.g. event types, user roles) in a shared union to avoid repetition.
• Combine with isMatch to get a reusable type guard: const isWrite = P.isMatch(P.union("POST", "PUT")).
• Patterns are evaluated in the order provided; place the most specific ones first if an expensive predicate calculation is present.

See also

• isMatch
• match
• when