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[spec] conceptual foundation and glossary entries for variance

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Documentation
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
documentation

Research direction

Start with the spec's section on variance and the existing core concepts section, then compare the rationale in PEP 483 and the linked Wikipedia article. Done means the variance section derives its rationale from the core concepts and the glossary defines invariant, covariant, contravariant, and variance.

Written by the indexing model from the issue text.

Description

topic: typing spec

Currently the section on variance says:

A longer introduction to these concepts can be found on Wikipedia and in PEP 483; here we just show how to control a type checker’s behavior.

Now that we have a core concepts section in the spec, it would be good for the spec to also derive the rationale for variance from those core concepts, rather than deferring to the (ten-year-old and not updatable) PEP 483.

We should also add glossary entries for variance terminology: invariant, covariant, contravariant, and variance.

Dominant language
Python
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Merged PRs (30d)
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