问题描述
使用新的 c# 7 元组语法，是否可以指定一个带有元组作为参数的 lambda，并在 lambda 中使用未打包的值?
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?
例子:
var list = new List<(int,int)>();
在 lambda 中使用元组的常规方法:
normal way to use a tuple in lambda:
list.Select(value => value.Item1*2 + value.Item2/2);
我希望一些新的糖可以避免 .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.
我在 lambda 定义中尝试了双括号，但没有成功:((x,y)) =>...，也许尝试起来很愚蠢，但双括号实际上在这里工作:
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，我的问题不完全是关于避免丑陋的默认名称 .Item .Item2，而是关于在 lambda 中实际解包元组(也许是为什么它没有实现或不可能).如果您来这里是为了解决默认名称，请阅读 Sergey Berezovskiy 的回答.
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:
刚刚想到一个更一般的用例:是否可以(或为什么不)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; }
而不是这个:
void Foo((int x,int y) value) { value.x+value.y }
推荐答案
如你所见，对于:
var list = new List<(int,int)>();
至少希望能够做到以下几点:
One would at least expect to be able to do the following:
list.Select((x,y) => x*2 + y/2);
但 C# 7 编译器(尚)不支持这一点.期望糖能够满足以下条件也是合理的:
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]);
编译器将 Foo(list[0]); 自动转换为 Foo(list[0].Item1, list[0].Item2);.
with the compiler converting Foo(list[0]); to Foo(list[0].Item1, list[0].Item2); automatically.
这些目前都不可能.但是，提案:lambda 参数列表中的元组解构 问题存在于 dotnet/cshaplang GitHub 上的 repo，要求语言团队考虑这些功能以用于 C# 的未来版本.如果您也希望看到对此的支持，请务必将您的声音添加到该线程.
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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