mirror of
https://github.com/astral-sh/ruff.git
synced 2025-08-03 18:28:24 +00:00
6d56ee803e
## Summary Part of [#117](https://github.com/astral-sh/ty/issues/117). `TypeIs[]` is a special form that allows users to define their own narrowing functions. Despite the syntax, `TypeIs` is not a generic and, on its own, it is meaningless as a type. [Officially](https://typing.python.org/en/latest/spec/narrowing.html#typeis), a function annotated as returning a `TypeIs[T]` is a <i>type narrowing function</i>, where `T` is called the <i>`TypeIs` return type</i>. A `TypeIs[T]` may or may not be bound to a symbol. Only bound types have narrowing effect: ```python def f(v: object = object()) -> TypeIs[int]: ... a: str = returns_str() if reveal_type(f()): # Unbound: TypeIs[int] reveal_type(a) # str if reveal_type(f(a)): # Bound: TypeIs[a, int] reveal_type(a) # str & int ``` Delayed usages of a bound type has no effect, however: ```python b = f(a) if b: reveal_type(a) # str ``` A `TypeIs[T]` type: * Is fully static when `T` is fully static. * Is a singleton/single-valued when it is bound. * Has exactly two runtime inhabitants when it is unbound: `True` and `False`. In other words, an unbound type have ambiguous truthiness. It is possible to infer more precise truthiness for bound types; however, that is not part of this change. `TypeIs[T]` is a subtype of or otherwise assignable to `bool`. `TypeIs` is invariant with respect to the `TypeIs` return type: `TypeIs[int]` is neither a subtype nor a supertype of `TypeIs[bool]`. When ty sees a function marked as returning `TypeIs[T]`, its `return`s will be checked against `bool` instead. ty will also report such functions if they don't accept a positional argument. Addtionally, a type narrowing function call with no positional arguments (e.g., `f()` in the example above) will be considered invalid. ## Test Plan Markdown tests. --------- Co-authored-by: Carl Meyer <carl@astral.sh> |
||
|---|---|---|
| .. | ||
| annotations | ||
| assignment | ||
| binary | ||
| boolean | ||
| boundness_declaredness | ||
| call | ||
| class | ||
| comparison | ||
| comprehensions | ||
| conditional | ||
| declaration | ||
| diagnostics | ||
| directives | ||
| doc | ||
| exception | ||
| expression | ||
| function | ||
| generics | ||
| ide_support | ||
| import | ||
| literal | ||
| loops | ||
| narrow | ||
| regression | ||
| scopes | ||
| shadowing | ||
| snapshots | ||
| stubs | ||
| subscript | ||
| suppressions | ||
| type_compendium | ||
| type_of | ||
| type_properties | ||
| type_qualifiers | ||
| unary | ||
| with | ||
| .mdformat.toml | ||
| attributes.md | ||
| cycle.md | ||
| dataclass_transform.md | ||
| dataclasses.md | ||
| decorators.md | ||
| del.md | ||
| descriptor_protocol.md | ||
| final.md | ||
| intersection_types.md | ||
| invalid_syntax.md | ||
| known_constants.md | ||
| mdtest_config.md | ||
| mdtest_custom_typeshed.md | ||
| metaclass.md | ||
| mro.md | ||
| named_tuple.md | ||
| overloads.md | ||
| pep695_type_aliases.md | ||
| properties.md | ||
| protocols.md | ||
| slots.md | ||
| statically_known_branches.md | ||
| sys_platform.md | ||
| sys_version_info.md | ||
| terminal_statements.md | ||
| type_api.md | ||
| typed_dict.md | ||
| union_types.md | ||
| unpacking.md | ||
| unreachable.md | ||