Type Alias AssertionGuard<T>

AssertionGuard: (input: unknown) => asserts input is T

Type definition for assertion guard functions in typia.

An assertion guard is a function that asserts an input value's type at runtime and performs a TypeScript type assertion if validation passes. Unlike regular assertion functions that return the validated value, assertion guards return nothing but automatically cast the input parameter to the expected type T.

This type is used by typia.createAssertGuard<T>() and typia.createAssertGuardEquals<T>() to generate reusable assertion guard functions.

Type Parameters

T
The expected type to validate and assert against

Type declaration

- (input: unknown): asserts input is T
- Parameters
  - input: unknown
    The value to validate (type unknown)
  Returns asserts input is T
  void - Returns nothing, but asserts that input is type T

Throws

When the input value doesn't match the expected type T

Example

interface IMember {
  name: string;
  age: number;
}

// Create reusable assertion guard
const assertMember: AssertionGuard<IMember> = typia.createAssertGuard<IMember>();

// Usage - input will be automatically cast to IMember if validation passes
const unknownData: unknown = { name: "John", age: 25 };

assertMember(unknownData);
// After this line, unknownData is automatically treated as IMember type
console.log(unknownData.name); // TypeScript knows this is safe

See

https://github.com/samchon/typia#assertguard-functions Typia assertion guards documentation
TypeGuardError Error thrown when assertion fails

Author

Jeongho Nam - https://github.com/samchon