C＃7元组和Lambda [英] C# 7 tuples and lambdas
问题描述
使用新的c＃7元组语法，是否可以指定一个以元组为参数的lambda并在lambda中使用解压缩的值？
With new c# 7 tuple syntax, is it possible to specify a lambda with a tuple as parameter and use unpacked values inside the lambda?
示例：
var list = new List<(int,int)>();
在lambda中使用元组的正常方法：
normal way to use a tuple in lambda:
list.Select(value => value.Item1*2 + value.Item2/2);
我希望有一些新糖可以避免 .Item1 .Item2 ，例如：
i expected some new sugar to avoid .Item1 .Item2, like:
list.Select((x,y) => x*2 + y/2);
最后一行不起作用，因为它被视为lambda的两个参数。我不确定是否有办法真正做到这一点。
The last line does not work because it is treated as two parameters for lambda. I am not sure if there is a way to do it actually.
编辑：
我尝试了双亲在lambda定义中不起作用：（（x，y））=> ... ，也许尝试起来很愚蠢，但是双括号实际上在这里起作用：
I tried double parentesis in lambda definition and it didn't work: ((x,y)) => ..., and maybe it was stupid to try, but double parenthesis actually work here:
list.Add((1,2));
另外，我的问题不是避免使用丑陋的默认名称 .Item。 Item2 ，这是关于在lambda中实际打开一个元组的包装（以及可能为什么不实现或不可能实现）。如果您是来这里使用默认名称的解决方案，请阅读 Sergey Berezovskiy的答案。
Also, my question is not quite about avoiding ugly default names .Item .Item2, it is about actual unpacking a tuple in lambda (and maybe why it's not implemented or not possible). If you came here for a solution to default names, read Sergey Berezovskiy's answer.
编辑2：
只是想到了一个更通用的用例：是否有可能（或为什么不能）解构传递给方法的元组？像这样：
Just thought of a more general use case: is it possible (or why not) to "deconstruct" tuple passed to a method? Like this:
void Foo((int,int)(x,y)) { x+y; }
代替此：
void Foo((int x,int y) value) { value.x+value.y }
推荐答案
如您所见，
var list = new List<(int,int)>();
一个人至少可以做到以下几点：
One would at least expect to be able to do the following:
list.Select((x,y) => x*2 + y/2);
但是C＃7编译器（尚）不支持此功能。希望糖允许以下情况也是合理的：
But the C# 7 compiler doesn't (yet) support this. It is also reasonable to desire sugar that would allow the following:
void Foo(int x, int y) => ...
Foo(list[0]);
，其中编译器将 Foo（list [0]）; 到 Foo（list [0] .Item1，list [0] .Item2）; 自动。
with the compiler converting Foo(list[0]); to Foo(list[0].Item1, list[0].Item2); automatically.
目前都不可行。但是，问题建议：lambda参数列表中的元组解构，存在于<$ GitHub上的c $ c> dotnet / csharplang 仓库，要求语言团队考虑将这些功能用于将来的C＃版本。如果您也希望看到对此的支持，请不要在该主题中添加您的声音。
Neither of these is currently possible. However, the issue, Proposal: Tuple deconstruction in lambda argument list, exists on the dotnet/csharplang repo on GitHub, requesting that the language team consider these features for a future version of C#. Please do add your voices to that thread if you too would like to see support for this.
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