API reference / @evolu/common / Type / UnionType

Interface: UnionType<Members>

Defined in: packages/common/src/Type.ts:3048

UnionType extends Type with an additional members property for reflection.

Extends

• Type<"Union", InferType<Members[number]>, InferInput<Members[number]>, UnionError<InferErrors<Members[number]>>, InferInput<Members[number]>, never>

Type Parameters

Type Parameter
Members extends [AnyType, ...ReadonlyArray<AnyType>]

Properties

Property	Modifier	Type	Description	Inherited from	Defined in
[EvoluTypeSymbol]	readonly	true	-	Type.[EvoluTypeSymbol]	packages/common/src/Type.ts:315
~standard	readonly	Props<InferInput<Members[number]>, InferType<Members[number]>>	The Standard Schema properties.	Type.~standard	packages/common/src/Type.ts:4216
Error	public	UnionError<InferErrors<Members[number]>>	The specific error introduced by this Type. ### Example type StringError = typeof String.Error;	Type.Error	packages/common/src/Type.ts:197
Errors	readonly	UnionError<InferErrors<Members[number]>>	Error / ParentError ### Example type StringParentErrors = typeof String.Errors;	Type.Errors	packages/common/src/Type.ts:381
from	readonly	(value) => Result<InferType<Members[number]>, UnionError<InferErrors<Members[number]>>>	Creates T from an Input value. This is useful when we have a typed value. from is a typed alias of fromUnknown.	Type.from	packages/common/src/Type.ts:212
fromParent	readonly	(value) => Result<InferType<Members[number]>, UnionError<InferErrors<Members[number]>>>	Creates T from Parent type. This function skips parent Types validations when we have already partially validated value.	Type.fromParent	packages/common/src/Type.ts:292
fromUnknown	readonly	(value) => Result<InferType<Members[number]>, UnionError<InferErrors<Members[number]>>>	Creates T from an unknown value. This is useful when a value is unknown.	Type.fromUnknown	packages/common/src/Type.ts:284
Input	public	InferInput<Members[number]>	The type expected by from and fromUnknown. ### Example type StringInput = typeof String.Input;	Type.Input	packages/common/src/Type.ts:195
is	readonly	(value) => value is InferType<Members[number]>	A type guard that checks whether an unknown value satisfies the Type. ### Example const value: unknown = "hello"; if (String.is(value)) { // TypeScript now knows valueis astring here. console.log("This is a valid string!"); } const strings: unknown[] = [1, "hello", true, "world"]; const filteredStrings = strings.filter(String.is); console.log(filteredStrings); // ["hello", "world"]	Type.is	packages/common/src/Type.ts:313
members	readonly	Members	-	-	packages/common/src/Type.ts:3057
name	readonly	"Union"	-	Type.name	packages/common/src/Type.ts:203
orNull	readonly	(value) => | InferType<Members[number]> | null	Creates T from an Input value, returning null if validation fails. This is a convenience method that combines from with getOrNull. When to use: - When you need to convert a validation result to a nullable value - When the error is not important and you just want the value or nothing - APIs that expect T or null ### Example // ✅ Good: Optional user input const age = PositiveInt.orNull(userInput); if (age != null) { console.log("Valid age:", age); } // ✅ Good: Default fallback const maxRetries = PositiveInt.orNull(config.retries) ?? 3; // ❌ Avoid: When you need to know why validation failed (use from instead) const result = PositiveInt.from(userInput); if (!result.ok) { console.error(formatPositiveError(result.error)); }	Type.orNull	packages/common/src/Type.ts:277
orThrow	readonly	(value) => InferType	Creates T from an Input value, throwing an error if validation fails. This is a convenience method that combines from with getOrThrow. When to use: - Configuration values that are guaranteed to be valid (e.g., hardcoded constants) - Application startup where failure should crash the program - Test code with known valid inputs ### Example // ✅ Good: Known valid constant const maxRetries = PositiveInt.orThrow(3); // ✅ Good: App configuration that should crash on invalid values const appName = SimpleName.orThrow("MyApp"); // ❌ Avoid: User input (use from instead) const userAge = PositiveInt.orThrow(userInput); // Could crash! // ✅ Better: Handle user input gracefully const ageResult = PositiveInt.from(userInput); if (!ageResult.ok) { // Handle validation error }	Type.orThrow	packages/common/src/Type.ts:245
Parent	public	InferInput<Members[number]>	The parent type. ### Example type StringParent = typeof String.Parent;	Type.Parent	packages/common/src/Type.ts:199
ParentError	public	never	The parent's error. ### Example type StringParentError = typeof String.ParentError;	Type.ParentError	packages/common/src/Type.ts:201
Type	readonly	InferType	The type this Type resolves to. ### Example type String = typeof String.Type;	Type.Type	packages/common/src/Type.ts:326