Class RequiresContext

returns/context/requires_context.py:44–443

The ``RequiresContext`` container. It's main purpose is to wrap some specific function and to provide tools to compose other functions around it without actually calling it. The ``RequiresContext`` container passes the state you want to share between functions. Functio

@final
class RequiresContext(  # type: ignore[type-var]
    BaseContainer,
    SupportsKind2['RequiresContext', _ReturnType_co, _EnvType_contra],
    reader.ReaderBased2[_ReturnType_co, _EnvType_contra],
):
    """
    The ``RequiresContext`` container.

    It's main purpose is to wrap some specific function
    and to provide tools to compose other functions around it
    without actually calling it.

    The ``RequiresContext`` container passes the state
    you want to share between functions.
    Functions may read that state, but can't change it.
    The ``RequiresContext`` container
    lets us access shared immutable state within a specific context.

    It can be used for lazy evaluation and typed dependency injection.

    ``RequiresContext`` is used with functions that never fail.
    If you want to use ``RequiresContext`` with returns ``Result``
    then consider using ``RequiresContextResult`` instead.

    Note:
        This container does not wrap ANY value. It wraps only functions.
        You won't be able to supply arbitrary types!

    See also:
        - https://dev.to/gcanti/getting-started-with-fp-ts-reader-1ie5
        - https://en.wikipedia.org/wiki/Lazy_evaluation
        - https://bit.ly/2R8l4WK

    """

    __slots__ = ()

    #: This field has an extra 'RequiresContext' just because `mypy` needs it.
    _inner_value: Callable[[_EnvType_contra], _ReturnType_co]

    #: A convenient placeholder to call methods created by `.from_value()`:
    no_args: ClassVar[NoDeps] = object()

    def __init__(
        self,
        inner_value: Callable[[_EnvType_contra], _ReturnType_co],
    ) -> None:
        """
        Public constructor for this type. Also required for typing.

        Only allows functions of kind ``* -> *``.

        .. code:: python

          >>> from returns.context import RequiresContext
          >>> str(RequiresContext(lambda deps: deps + 1))
          '<RequiresContext: <function <lambda> at ...>>'