57 lines
1.7 KiB
Markdown
57 lines
1.7 KiB
Markdown
# C# Language Design Notes for August 22, 2018
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# Agenda
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1. Target-typed new
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1. Clarification on constraints with nullable reference types enabled
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# Discussion
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## Target-typed new
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Proposal: https://github.com/dotnet/csharplang/blob/master/proposals/target-typed-new.md
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*Question: Should target-typed `new` be allowed for tuple types?*
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We currently don't allow the constructor syntax `new (int, int)(0, 0)`.
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Should we allow `(int, int) t = new(0, 0)`? Would this mean the same thing as
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a tuple literal, or a call to a constructor on System.ValueTuple? This would
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also expose some of the differences between ValueTuple and tuple types, in
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that there is no constructor for a tuple type with greater than 7 elements.
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Decision: Let's allow it, as long as that doesn't require a lot of extra
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work. The meaning would be to call the underlying System.ValueTuple
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constructors. This would expose differences in tuples with a lot of elements,
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but this seems like a very rare and unimportant case.
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*Question: Allow `throw new()`? It would convert to bare `Exception` by the spec.*
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Decision: Disallow. Fundamentally, we don't like this stylistically.
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*Question: Allow `new()` with user-defined comparison and arithmetic operators?*
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Decision: Allow.
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## Generic constraints with nullable reference types
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*Question: In the following snippet, is `U` a non-nullable reference type?*
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```C#
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void M<T, U>() where T : class, U : T` {}
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```
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Answer: Yes
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*Question: In the following snippet, is `I` a non-nullable reference type?*
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```C#
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interface I {}
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void M<T>() where T : I {}
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```
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Answer: Yes
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*Q: Do we want to warn for redundant constraints?*
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A: We don't currently. Let's stay with that decision for now. |