Combine switch expression with let keyword

[Khaos66]

It would be cool if it was possible to assign a new variable before the switch case expression is evaluated.
Something like this:

var result = value switch {
   string let var s = value.ToString() => s[..s.IndexOf('x')],
   _ => null
}

This is just a very simple example. Of course the let expression and case expressions can be more complex.
But this demonstrates, that s is used multiple times inside the case expression and with a let expression ToString() is only needed once.

Whats your oppinion on this?

[YairHalberstadt]

You can currently do:

var result = value switch {
   string s => s[..s.IndexOf('x')],
   _ => null
}

[Khaos66]

Yes you're right. But as I sad the let could be something completely different. I just choose ToString, as it's simple to understand.
Here is a different example:

var result = type switch {
   Enum.TypeString let var s = value.ToString() => s[..s.IndexOf('x')],
   _ => null
}

This is actually more what I'm facing right now.

[Khaos66]

The best way to do this right now would be to call a method

string ConvertStr(string s) => s[..s.IndexOf('x')];

var result = type switch {
   Enum.TypeString => ConvertStr(value.ToString()),
   _ => null
}

So this is achievable right now. But I still want to leave the discussion open

[YairHalberstadt]

You can currently do this:

var result = type switch {
   object o when o.ToString() is var s => s[..s.IndexOf('x')],
   _ => null
}

[stepanbenes]

string let var s

This is brilliant.

[YairHalberstadt]

With #3037 you would be able to do:

var result = type switch {
   Enum.TypeString value => {
       var s = value.ToString();
       s[..s.IndexOf('x')]
   },
   _ => null
}

[Khaos66]

Also acceptable ;)