[API Proposal]: Add [Try]Parse to Rune

[koszeggy]

Background and motivation

In many aspects Rune is similar to char, it has also the same formatting features, still, it does not support parsing.

As a workaround, one can use the following solution:

private static bool TryParseRune(string s, out Rune value)
{
    if (s == null)
        throw new ArgumentNullException(nameof(s));
    if (Rune.TryGetRuneAt(s, 0, out Rune rune) && rune.Utf16SequenceLength == s.Length)
    {
        value = rune;
        return true;
    }

    value = default;
    return false;
}

But unfortunately TryGetRune has no overloads for ReadOnlySpan<char> so the span version of the workaround should either to use SpanRuneEnumerator or some switch over the length of the span.

Interestingly enough, Rune implements IUtf8SpanParsable<Rune> lately (only explicitly though), but not IParsable<Rune> and ISpanParsable<Rune>.

API Proposal

public struct Rune : IComparable, IComparable<Rune>, IEquatable<Rune>
     , IUtf8SpanFormattable, IUtf8SpanParsable<Rune> // added in .NET 8
+    , IParsable<Rune>, ISpanParsable<Rune> 
{
+    public static Rune Parse(string s, IFormatProvider? provider);
+    public static bool TryParse(string s, IFormatProvider? provider, out Rune result);

+    public static Rune Parse(ReadOnlySpan<char> s, IFormatProvider? provider);
+    public static bool TryParse(ReadOnlySpan<char> s, IFormatProvider? provider, out Rune result);
}

API Usage

// Explicit usage example
var r1 = Rune.Parse("🙂");
bool success = Rune.TryParse("👀", out Rune r2);

// Interface usage example
static T Parse<T>(string s) where T : IParseable<T> => T.Parse(s);
var r3 = Parse<Rune>("😎");

Risks

I don't see any. But to be really similar to char maybe a RuneConverter could also be necessary to be able convert to and from string in already existing libraries (eg. XML/JSON serializers, etc.)

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Issue Details

---

Background and motivation

In many aspects Rune is similar to char, it has also the same formatting features, still, it does not support parsing.

As a workaround, one can use the following solution:

private static bool TryParseRune(string s, out Rune value)
{
    if (s == null)
        throw new ArgumentNullException(nameof(s));
    if (Rune.TryGetRuneAt(s, 0, out Rune rune) && rune.Utf16SequenceLength == s.Length)
    {
        value = rune;
        return true;
    }

    value = default;
    return false;
}

But unfortunately TryGetRune has no overloads for ReadOnlySpan<char> so the span version of the workaround should either use enumarator or some switch over the length of the span.

An additional motivation would be to be include the Rune type into the set of IParseable<TSelf> types

API Proposal

public struct Rune : IComparable, IComparable<Rune>, IEquatable<Rune>, ISpanFormattable
+    , IBinaryInteger<Rune>, IMinMaxValue<Rune>, IUnsignedNumber<Rune>
{
+    Rune Parse(string s[, ...]);
+    Rune Parse(ReadOnlySpan<char> s[, ...]);
+    bool TryParse(string s[, ...], out Rune value);
+    bool TryParse(ReadOnlySpan<char> s[, ...], out Rune value);
+    // and the interface implementations
}

API Usage

// Explicit usage example
var r1 = Rune.Parse("🙂");
bool success = Rune.TryParse("👀", out Rune r2);

// Interface usage example
static T Parse<T>(string s) where T : IParseable<T> => T.Parse(s);
var r3 = Parse<Rune>("😎");

Risks

I don't see any. But to be really similar to char maybe a RuneConverter could also be necessary to be able convert to and from string in already existing libraries (eg. XML/JSON serializers, etc.)

Author:	koszeggy
Assignees:	-
Labels:	api-suggestion, area-System.Runtime, untriaged
Milestone:	-

[koszeggy]

I'm pinging this to prevent from cleaning up.

[tannergooding]

@koszeggy, if you can update the proposal to only include IParsable and ISpanParsable then I can mark this ready for review.

Rune cannot implement the full numeric interfaces as it is not a numeric type and explicitly doesn't allow any bit-pattern. Bad things can happen if you have an ill-formed Rune and so users should just work with the Value property and create a new rune when done with their arithmetic or bitwise operations.

[koszeggy]

I updated the OP.

Rune cannot implement the full numeric interfaces as it is not a numeric type and explicitly doesn't allow any bit-pattern.

Understood. I took char as a base, without thinking twice why it could implement all those interfaces.