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Showing content from https://github.com/dotnet/csharplang/issues/1881 below:

Switching ReadOnlySpan<char> with constant strings · Issue #1881 · dotnet/csharplang · GitHub

Speclet: https://github.com/dotnet/csharplang/blob/main/proposals/csharp-11.0/pattern-match-span-of-char-on-string.md

With the recent addition of Spans, we can reduce a lot of allocations when dealing with strings. For example, substrings can be replaced with slices. However, there is one place where using strings is better:

string str = ...;
switch (str)
{
    case "string 1":
        break;
    case "string 2":
        break;
    case "string 3":
        break;
    case "string 4":
        break;
}

With spans, you are forced to write boilerplate code:

ReadOnlySpan<char> span = ...;
switch (span)
{
    case var _ where span == "string 1":
        break;
    case var _ where span == "string 2":
        break;
    case var _ where span == "string 3":
        break;
    case var _ where span == "string 4":
        break;
}

Which is identical to the if-else mess that switches aim to solve.

ReadOnlySpan<char> span = ...;
if (span == "string 1")
else if (span == "string 2")
else if (span == "string 3")
else if (span == "string 4")

It would be better if spans can be switched with constant strings.

ReadOnlySpan<char> span = ...;
switch (span)
{
    case "string 1":
        break;
    case "string 2":
        break;
    case "string 3":
        break;
    case "string 4":
        break;
}

Special-casing spans as a compiler-known type already have precedent in stackalloc expressions, it can also be done here.
Possible extension to regular Span<char> can also be considered, but it is not as important as ReadOnlySpan<char>. We could also enable this with ReadOnlyMemory<char> and Memory<char>.

More possible extensions: switching (ReadOnly)Span<char> with char, (ReadOnly)Span<T> with T where T is a constant type.

https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-02-23.md#pattern-matching-over-spanchar

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