Span<T> Hacks

SpanHacks.cs

/// <summary>
/// INTERNAL API.
///
/// <see cref="Span{T}"/> polyfills that should be deleted once we drop .NET Standard 2.0 support.
/// </summary>
internal static class SpanHacks
{
    public static bool IsNumeric(char x)
    {
        return (x >= '0' && x <= '9');
    }

    /// <summary>
    /// Parses an integer from a string.
    /// </summary>
    /// <remarks>
    /// PERFORMS NO INPUT VALIDATION.
    /// </remarks>
    /// <param name="str">The span of input characters.</param>
    /// <returns>An <see cref="int"/>.</returns>
    public static int Parse(ReadOnlySpan<char> str)
    {
        if (TryParse(str, out var i))
            return i;
        throw new FormatException($"[{str.ToString()}] is now a valid numeric format");
    }

    /// <summary>
    /// Parses an integer from a string.
    /// </summary>
    /// <remarks>
    /// PERFORMS NO INPUT VALIDATION.
    /// </remarks>
    /// <param name="str">The span of input characters.</param>
    /// <param name="returnValue">The parsed integer, if any.</param>
    /// <returns>An <see cref="int"/>.</returns>
    public static bool TryParse(ReadOnlySpan<char> str, out int returnValue)
    {
        var pos = 0;
        returnValue = 0;
        var sign = 1;
        if (str[0] == '-')
        {
            sign = -1;
            pos++;
        }

        for (; pos < str.Length; pos++)
        {
            if (!IsNumeric(str[pos]))
                return false;
            returnValue = returnValue * 10 + str[pos] - '0';
        }

        returnValue = sign * returnValue;

        return true;
    }

    /// <summary>
    /// Performs <see cref="string.ToLowerInvariant"/> without having to
    /// allocate a new <see cref="string"/> first.
    /// </summary>
    /// <param name="input">The set of characters to be lower-cased</param>
    /// <returns>A new string.</returns>
    public static string ToLowerInvariant(ReadOnlySpan<char> input)
    {
        Span<char> output = stackalloc char[input.Length];
        for (var i = 0; i < input.Length; i++)
        {
            output[i] = char.ToLowerInvariant(input[i]);
        }
        return output.ToString();
    }
}

Added TryParse method in addition to the original Parse routine for int extraction