Function ezno_checker::types::subtyping::type_is_subtype

source · 
pub fn type_is_subtype(
    base_type: TypeId,
    ty: TypeId,
    state: &mut State<'_>,
    environment: &Environment<'_>,
    types: &TypeStore
) -> SubTypeResult
Expand description

Checks whether ty is a subtype of the base_type

  • equivalently …base_type :>= ty (ty <=: base_type)
  • equivalently … whether ty could be substituted as base_type.
  • equivalently … whether ty’s properties imply the existence of base_type properties.
Examples found in repository?
examples/calculate_subtypes.rs (line 99)
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fn contributions(environment: &mut Environment, types: &mut TypeStore) {
	// TODO types API, which doesn't is less hand-holdy
	let generic_parameter =
		environment.new_explicit_type_parameter("T", Some(TypeId::NUMBER_TYPE), None, types);

	// create `{}` and add `inner: T`
	let object = types.new_anonymous_interface_type();
	let inner = PropertyKey::String(std::borrow::Cow::Owned("inner".to_owned()));
	environment.info.register_property(
		object,
		Publicity::Public,
		inner.clone(),
		PropertyValue::Value(generic_parameter.type_id),
		false,
		source_map::SpanWithSource::NULL,
	);

	let or = types.new_or_type(generic_parameter.type_id, object);
	let parameter = types.new_function_parameter(or);

	let five = types.new_constant_type(Constant::Number(5f64.try_into().unwrap()));

	let five_obj = {
		let mut basis = ObjectBuilder::new(
			None,
			types,
			source_map::SpanWithSource::NULL,
			&mut environment.info,
		);
		basis.append(
			environment,
			Publicity::Public,
			inner,
			PropertyValue::Value(five),
			source_map::SpanWithSource::NULL,
		);
		basis.build_object()
	};

	// x(5)
	{
		let contributions = Contributions::default();
		let mut state = State {
			already_checked: Default::default(),
			mode: Default::default(),
			contributions: Some(contributions),
			others: SubTypingOptions::default(),
			object_constraints: None,
		};
		let result = type_is_subtype(parameter, five_obj, &mut state, &environment, &types);

		let contributions = state.contributions.as_ref().unwrap();

		eprintln!(
			"{:?}:>{:?}
result={:?}
staging_covariant={:?}
staging_contravariant={:?}",
			parameter,
			five,
			result,
			contributions.staging_covariant,
			contributions.staging_contravariant
		);
	}
}