ts-data-forge
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text/typescript
/**
* Compile-time type assertion utility for TypeScript type testing.
*
* This function performs static type relationship checking at compile-time and
* has no runtime effect. It is primarily used in test files to verify that
* TypeScript's type inference and type relationships work as expected. The
* function will cause TypeScript compilation errors if the specified type
* relationship does not hold.
*
* ## Supported Type Relations
*
* ### Equality Relations
*
* - **`"="` (strict equality)**: Asserts that types `A` and `B` are exactly the
* same type. Uses TypeScript's internal type equality checking.
* - **`"!="` (strict inequality)**: Asserts that types `A` and `B` are not
* exactly the same type.
*
* ### Assignability Relations
*
* - **`"~="` (mutual assignability)**: Asserts that `A` extends `B` AND `B`
* extends `A`. Types are structurally equivalent and mutually assignable.
* - **`"<="` (subtype relation)**: Asserts that type `A` extends (is assignable
* to) type `B`. Type `A` is a subtype of `B`.
* - **`">="` (supertype relation)**: Asserts that type `B` extends (is assignable
* to) type `A`. Type `A` is a supertype of `B`.
*
* ### Negative Assignability Relations
*
* - **`"!<="` (not subtype)**: Asserts that type `A` does NOT extend type `B`.
* - **`"!>="` (not supertype)**: Asserts that type `B` does NOT extend type `A`.
*
* ## Type Parameter Constraints
*
* @since 1.0.0
* @template A - The first type for comparison. Can be any TypeScript type
* including:
*
* - Primitive types (string, number, boolean, etc.)
* - Object types and interfaces
* - Union and intersection types
* - Generic types and type parameters
* - Literal types and branded types
* - Function types and return types
*
* @template B - The second type for comparison. Same constraints as type `A`.
* @param _relation - A string literal representing the expected type
* relationship. TypeScript's type system automatically infers and restricts
* the available operators based on the actual relationship between types `A`
* and `B`. If an invalid relationship is specified, TypeScript will show a
* compilation error.
*
* Combine `expectType` with runtime assertions for comprehensive testing:
*
* ## Important Notes
*
* - **Compile-time only**: This function has no runtime behavior and will be
* optimized away.
* - **Type inference**: The available relation operators are automatically
* inferred by TypeScript based on the actual type relationship between
* `A` and `B`.
* - **Error feedback**: Invalid type relationships will cause clear TypeScript
* compilation errors.
* - **Test organization**: Typically used in `.test.mts` files alongside runtime
* assertions.
* - **Performance**: Has zero runtime overhead as it's purely a compile-time
* construct.
*/
export declare const expectType: <A, B>(_relation: TypeEq<A, B> extends true ? "<=" | "=" | ">=" | "~=" : "!=" | (TypeExtends<A, B> extends true ? "<=" | (TypeExtends<B, A> extends true ? ">=" | "~=" : "!>=") : "!<=" | (TypeExtends<B, A> extends true ? ">=" : "!>="))) => void;
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