[Requirement] Param class and common implementations

[SimonHeybrock]

Executive summary

For auto-generating workflow parameter input widgets, a base class and implementations for common param types are needed

Context and background knowledge

See #28. Have a look at, e.g., https://docs.mantidproject.org/v6.1.0/algorithms/LoadEventNexus-v1.html. The widget and the table of properties in the docs page was generated programmatically. Each line corresponds to a "param" as described here (Mantid calls these "algorithm properties").

Inputs

The param classes will have a number of required and optional inputs. Something like:

Required:

• Name
• Description
• Type
• Required
• Default value

Optional:

• Bounds
• Validators

Methodology

The Param base class (working title) should run things such as validators.

Outputs

Implementations of the Param class must be able to construct a simple widget that can be included in higher-level widgets as part of #28.

Examples of required Param implementations:

• BinEdgeParam (linear/log, start, stop, num, unit, ...)
• Boolean, integer, ...
• Scalar (float) with unit
• Filename/path

Which interfaces are required?

Python module / function

Test cases

Params for ESSsans inputs make a good scenario for prototyping and testing

Comments

• Feature: Generate Python code from param class with set values.

[jl-wynen]

See also https://github.com/scipp/sciline/issues/139 for a discussion and prototypes.

[SimonHeybrock]

See also scipp/sciline#139 for a discussion and prototypes.

Note that the Param described in the requirement does not need any relation/interaction with Sciline, unlike in the linked issue.