Cache default(TResult) values

[cmeeren]

Fixes #523

Details on the issue fix or feature implementation

I have not added any new unit tests, because I think it's adequately covered by the numerous adapted tests.

Confirm the following

• I have merged the latest changes from the dev vX.Y branch
• I have successfully run a local build
• I have included unit tests for the issue/feature
• I have targeted the PR against the latest dev vX.Y branch

[cmeeren]

Please review carefully, these are non-trivial changes to both code and tests.

Also, feel free to merge and make changes yourself if that's quicker/easier than having me update the PR.

[reisenberger]

Thanks @cmeeren . PR looks great! I am going to push four more tests which prove the default(TResult) cases work for an arbitrary cache provider (in other words, that Polly itself does not impose any limitations), for both get and put, for both value types and reference types.

Individual cache providers may of course impose their own limitations on caching null, but none (is my first initial guess...) will impose any limitation on caching default(TResult) for a value type.

Note: I am holding (not merging) this PR until we have ready the associated fixes to Polly cache providers and serialization providers:

• Adjust for v7.0 changes to Polly Polly.Caching.MemoryCache#30 ;
• Adjust for v7.0 changes to Polly Polly.Caching.IDistributedCache#10 ;
• Adjust for v7.0 changes to Polly Polly.Caching.Serialization.Json#10 .

But otherwise I think this PR (with extra tests I'll push) is good to go.

[reisenberger]

@cmeeren I'm merging this into the v7.0.0 dev branch now, as I've brought the cache providers and serializers into alignment with the v7.0 changes, in the following PRs:
(the PRs on those repos will not actually be merged until Polly v7.0.0 releases publicly)

• Version 3.0.0: For compatibility with (forthcoming) Polly v7.0.0 Polly.Caching.Serialization.Json#13
• Version 3.0.0: For compatibility with (forthcoming) Polly v7.0.0 Polly.Caching.MemoryCache#33
• Version 3.0.0: For compatibility with (forthcoming) Polly v7.0.0 Polly.Caching.IDistributedCache#13

Please feel free to review those PRs. Each cache provider repo now has integration tests proving we can round-trip cache or serialize a range of values across a range of types, including the default(TResult) case for value types which you originally raised.

Thanks for your contribution! You have credit in the readme!

[cmeeren]

Thanks, happy to help! :)

[reisenberger]

@cmeeren The change will release publicly to nuget when v7.0.0 releases. (Remaining work: documentation on the new custom policies and Simmy.)