80 lines
2.5 KiB
Markdown
80 lines
2.5 KiB
Markdown
# C# Language Design Notes for Oct 16, 2017
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***Warning: These are raw notes, and still need to be cleaned up. Read at your own peril!***
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"Being on the same floor as SPJ is a good way to shake out difficult corner cases"
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1. LINQ
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2. Shapes
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# Applying to LINQ
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Mixed results.
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Looking for perf, and ways to do more selective specialization.
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## Sum
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Specialized to some numeric types, but not all. 500 lines of code. In those, the loop is unspecialized too.
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One page of code!
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A new design dimension: should I use interfaces or concepts: pay for abstraction or pay for specialization
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Generic soup: this may be a superficial design issue, or even tooling issue.
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For instance, the `AssociatedType`s, other languages allow them to be retrieved by dot notation. Jeremy Siek paper "Associated Types and ...". `TColl.TEnum` etc.
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From experience, abstracting over enumerators tends to need associated types or higher-kinded types.
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Shouldn't be too discouraged by being smoked by LINQOptimizer. That one optimizes big queries, but what keeps people away from LINQ is more the death by a thousand paper cuts of using LINQ all the time. Roslyn avoids things that allocate, which today means not using LINQ. THis could be the thing that would allow it to.
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## Select
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The return type is associated. The problem is that adding new instances can change the return type from afar, upsetting the consuming code.
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Improves by 2/3rds when the array specialization is used.
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## SelectMany
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The generic type inference gets very messy here. It shows that concept inference needs to be interleaved with type inference in a way that we are still only loosely grasping.
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This is a place where LINQ allocates a lot, whereas this allocates hardly anything. We go at .75 the time even unspecialized. Also, the specialized version is twice as fast as the unspecialized.
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It shows that if you open up for specializations to be plopped in, there's quite a lot to gain.
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## Conclusion
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Some promise on optimization. Pinches of salt here and there. The approach definitely seems to have promise.
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More tests to do.
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# Shapes
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Concepts can tie in to the richness of expression in C# around different kinds of operations (operators, conversions, constructors...)
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Interesting to consider whether there's more of a specialization relationship between concepts and instances, rather than a type/instance relationship.
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If this went further, there's a very large laundry list.
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# Conclusion
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We *really* would like to be able to do the post-hoc implementation of concepts. This
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