"""
Providing typing utilities.
"""
from __future__ import annotations
import re
from typing import TypeVar
_T = TypeVar("_T")
_INTERNAL_INDENTATION_PATTERN = re.compile(r"( +)")
def _internal(target: _T) -> _T:
doc = target.__doc__ or ""
doc_last_line = doc.rsplit("\n")[-1]
indentation_match = _INTERNAL_INDENTATION_PATTERN.match(doc_last_line)
indentation = indentation_match.group(0) if indentation_match else ""
target.__doc__ = (
doc
+ f"\n\n{indentation}This is internal. It **MAY** be used anywhere in Betty's source code, but **MUST NOT** be used by third-party code."
)
return target
[docs]
@_internal
def internal(target: _T) -> _T:
"""
Mark a target as internal to Betty.
Anything decorated with ``@internal`` MAY be used anywhere in Betty's source code,
but MUST be considered private by third-party code.
"""
return _internal(target)
[docs]
@internal
def public(target: _T) -> _T:
"""
Mark a target as publicly usable.
This is intended for items nested inside something marked with :py:func:`betty.typing.internal`,
such as class attributes: third-party code **SHOULD NOT** use a class marked ``@internal``
directly, but **MAY** use any of its attributes that are marked ``@public``.
"""
return target
[docs]
class Void:
"""
A sentinel that describes the absence of a value.
Using this sentinel allows for actual values to be ``None``. Like ``None``,
``Void`` is only ever used through its type, and never instantiated.
"""
[docs]
def __new__(cls): # pragma: no cover # noqa D102
raise RuntimeError("The Void sentinel cannot be instantiated.")