Do char based extension for StartsWith and EndsWith make sense for ReadOnlySpan<char>

[SimonCropp]

So this issue managed the addition of

 public static bool StartsWith(this ReadOnlySpan<char> span, ReadOnlySpan<char> value, StringComparison comparison);
 public static bool EndsWith(this ReadOnlySpan<char> span, ReadOnlySpan<char> value, StringComparison comparison);

but not the addition of

 public static bool StartsWith(this ReadOnlySpan<char> span, char value);
 public static bool EndsWith(this ReadOnlySpan<char> span, char value);

Am i missing something that would mean these methods dont make sense for ReadOnlySpan<char>?

[huoyaoyuan]

There are already overloads for generic T:

    public static class MemoryExtensions
    {
        public static bool Contains<T>(this ReadOnlySpan<T> span, T value)
            where T: IEquatable<T>;
    }

Note the IEquatabla<T> constraint.

[SimonCropp]

ahh u r correct. so it is only StartsWith/EndsWith that are missing. i will update the discussion

[colejohnson66]

Probably because those can be simply implemented as span.Length >= 1 && span[0] == value (or span[^1] for EndsWith).

If such methods were to be added, I'd argue they should be generic over T where T : IEquatable<T> like Contains is. In fact, those string ones could probably do the same. There's no reason StartsWith (where value is a span) should be limited to characters.

[wstaelens]

which one should be preferred:

ros.Length > 0 && ros[0] == 'a';

or

ros.Length >= 1 && ros[0] == 'a';

or

!ros.IsEmpty && ros[0] == 'a';

?

[neon-sunset]

You can also write ros is [.., 'a'] or ros is ['a', ..].

[MihaZupan]

I didn't realize this discussion existed already, but here's an API proposal issue for span StartsWith/EndsWith: #87689