.. _Typer Argument vs Option:

==================
Argument vs Option
==================
In Typer, there are two primary classes for providing CLI parameter configuration:

* ``Argument`` results in a positional CLI argument.

* ``Option`` results in a keyword CLI argument, preceded with a ``--``.

With more modern python type annotations, this distinction is unnecessary, because parameters (positional or keyword) can be determined directly from the function signature.

Consider the following function signatures:

.. code-block:: python

   def pos_or_keyword(a, b):
       pass

   def pos_only(a, b, /):
       pass

   def keyword_only(*, a, b=2):
       pass

   def mixture(a, /, b, *, c=3):
       pass

If you aren't familiar with these declarations, refer to the official PEP570_, or `a more user-friendly tutorial`_.

From these function signatures, we can deduce:

1. Which parameters are position-only, keyword-only, or both.

2. Which parameters are required, by their lack of defaults.

Because of these builtin python mechanisms, Cyclopts has a single :class:`Parameter <cyclopts.Parameter>` class used for providing additional parameter metadata.

I believe that Typer's separate ``Argument`` and ``Option`` classes are a relic from when they must be supplied as a parameter's proxy default value.

.. code-block:: python

   app = typer.Typer()

   @app.command()
   def foo(a=Argument(), b=Option(default=2)):
       pass

When used as such, we lose the ability to define the function signature with position-only or keyword-only markers.
We also lose the ability to directly inspect which parameters are optional by having "real" defaults and which ones are required.

.. _PEP570: https://peps.python.org/pep-0570/
.. _a more user-friendly tutorial: https://realpython.com/lessons/positional-only-arguments/
