.NET 8 未満向け MemoryExtensions.Split もどき

SpanSplitExtensions.cs

public static class SpanSplitExtensions {

    public static int Split<T>(this ReadOnlySpan<T> source, Span<Range> destination, T separator) where T: IEquatable<T> {
        return Split(source, destination, new ReadOnlySpan<T>(separator));
    }
    
    public static int Split<T>(this ReadOnlySpan<T> source, Span<Range> destination, ReadOnlySpan<T> separator) where T: IEquatable<T> {
        int rangesWritten = 0;
        
        int offset = 0;
        foreach (ref Range dest in destination) {
            if (rangesWritten + 1 == destination.Length) {
                dest = offset..;
                rangesWritten++;
                break;
            }
            
            int idx = source[offset..].IndexOf(separator);
            if (idx < 0) {
                dest = offset..;
                rangesWritten++;
                break;
            }
            
            dest = offset..(offset + idx);
            rangesWritten++;
            offset += idx + 1;
        }
        
        return rangesWritten;
    }
}

Usage.cs

ReadOnlySpan<char> payload = "a::bc:def";

Span<Range> ranges = stackalloc Range[3];
int rangesWritten = payload.Split(ranges, ':').Dump();
foreach (Range range in ranges[..rangesWritten]) {
    payload[range].ToString().Dump();
}

// 3
// a
// 
// bc:def