Value tuple type pattern

Question

I am trying to use a type pattern in C# 7 against a tuple type:

var lst = new List<object>();
lst.Add("foo");
lst.Add(("bar","baz"));

foreach (var item in lst) {
    switch (item) { 
        case string s:
            break;
        case (string, string) t: //Compiler error here
            break;
    }
}

but the compiler gives me the following error:

Invalid expression term 'string' A constant value is expected

How can I resolve this?

N.B. I know I can use:

case ValueTuple<string,string> t:

but I am wondering if there is a better syntax.

huysentruitw · Accepted Answer · 2017-08-08T18:20:57.917

4

Just use case ValueTuple<string, string> t:.

You just added the same solution to your question while I posted this answer. Well, you'll have to stick with this solution until they add compiler support for the case (,): syntax (wouldn't wait for that since this is an edge case).

edited Aug 08 '17 at 18:20

answered Aug 08 '17 at 18:09

huysentruitw

27,376
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score 1 · Answer 2 · answered Aug 27 '17 at 07:01

1

There are different sorts of patterns which were not implemented in C# 7.0, but are tracked in the patterns proposal, including recursive and positional patterns that you describe. Some of those are candidate for later 7.x point releases.

answered Aug 27 '17 at 07:01

Julien Couvreur

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Value tuple type pattern

2 Answers2