Mark Enumerable methods with the PureAttribute

[Evangelink]

Hello,

Looking at dotnet/roslyn-analyzers#3363 I have realized that the System.Linq.Enumerable methods are not marked with the PureAttribute which seems odd to me. Is there an obvious reason I am missing?

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[Evangelink]

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[stephentoub]

Mainly because [Pure] is part of the Contracts APIs, which we've stopped using in general across the core libraries. We've not gone through and purged existing usage of Pure, but we also haven't been adding it to new APIs in the last many years.

[Evangelink]

I see! I wasn't aware this was somehow "deprecated". Are you planning to have any kind of replacement? I see a lot of places where an attribute gives some metadata and helps building analyzers.

[stephentoub]

Are you planning to have any kind of replacement?

Not currently. Being able to reason about what kind of mutations code might or might not perform is certainly interesting, but it's also non-trivial; [Pure] only scraped the surface. For example, see the whole "Permissions" section in the write-up here: http://joeduffyblog.com/2016/11/30/15-years-of-concurrency/.

[eiriktsarpalis]

Great article, thanks for sharing.