C# 7 模式匹配元组 [英] C# 7 Pattern Match with a tuple

问题描述

是否可以像这样使用 c# 7 在 switch 语句中使用模式匹配的元组:

Is it possible to use tuples with pattern matching in switch statements using c# 7 like so:

switch (parameter)
{
   case ((object, object)) tObj when tObj.Item1 == "ABC":
        break;
}

我收到一个错误，指出 tObj 在当前上下文中不存在.

I get an error that says tObj does not exist in the current context.

我也试过这个:

switch (parameter)
{
   case (object, object) tObj when tObj.Item1 == "ABC":
        break;
}

这很好用:

switch (parameter)
{
   case MachineModel model when model.Id == "123":
        break;
}

推荐答案

记住 C#7 元组只是语法糖，所以 (object, object) 实际上只是 System.ValueTuple<对象，对象>.

Remember that C#7 tuples are just syntactic sugar, so (object, object) is really just System.ValueTuple<object, object>.

我猜开发团队在元组的新语法中没有考虑到这种特殊情况，但您可以这样做:

I guess that the dev team didn't take this particular situation into account for the new syntax for tuples, but you can do this:

switch (parameter)
{
    case System.ValueTuple<object, object> tObj when tObj.Item1 == "x":
        break;
}

此外，由于var 模式"将匹配任何内容并尊重类型，因此上述内容可以简化为:

Also, since the "var pattern" will match anything and respect the type, the above can be simplified to:

switch (parameter)
{
    case var tObj when tObj.Item1 == "x":
        break;
}

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