private static Rune ChangeCaseCultureAware(Rune rune, TextInfo textInfo, bool toUpper)
{
Debug.Assert(!GlobalizationMode.Invariant, "This should've been checked by the caller.");
Debug.Assert(textInfo != null, "This should've been checked by the caller.");
Span <char> original = stackalloc char[2]; // worst case scenario = 2 code units (for a surrogate pair)
Span <char> modified = stackalloc char[2]; // case change should preserve UTF-16 code unit count
int charCount = rune.EncodeToUtf16(original);
original = original.Slice(0, charCount);
modified = modified.Slice(0, charCount);
if (toUpper)
{
textInfo.ChangeCaseToUpper(original, modified);
}
else
{
textInfo.ChangeCaseToLower(original, modified);
}
// We use simple case folding rules, which disallows moving between the BMP and supplementary
// planes when performing a case conversion. The helper methods which reconstruct a Rune
// contain debug asserts for this condition.
if (rune.IsBmp)
{
return(UnsafeCreate(modified[0]));
}
else
{
return(UnsafeCreate(UnicodeUtility.GetScalarFromUtf16SurrogatePair(modified[0], modified[1])));
}
}
/// <summary>
/// Copies the characters from the source span into the destination, converting each character to lowercase,
/// using the casing rules of the specified culture.
/// </summary>
/// <param name="source">The source span.</param>
/// <param name="destination">The destination span which contains the transformed characters.</param>
/// <param name="culture">An object that supplies culture-specific casing rules.</param>
/// <remarks>If <paramref name="culture"/> is null, <see cref="System.Globalization.CultureInfo.CurrentCulture"/> will be used.</remarks>
/// <returns>The number of characters written into the destination span. If the destination is too small, returns -1.</returns>
/// <exception cref="InvalidOperationException">The source and destination buffers overlap.</exception>
public static int ToLower(this ReadOnlySpan <char> source, Span <char> destination, CultureInfo?culture)
{
if (source.Overlaps(destination))
{
throw new InvalidOperationException(SR.InvalidOperation_SpanOverlappedOperation);
}
if (culture == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.culture);
}
// Assuming that changing case does not affect length
if (destination.Length < source.Length)
{
return(-1);
}
if (GlobalizationMode.Invariant)
{
TextInfo.ToLowerAsciiInvariant(source, destination);
}
else
{
culture !.TextInfo.ChangeCaseToLower(source, destination); // TODO-NULLABLE: Remove ! when [DoesNotReturn] respected
}
return(source.Length);
}
/// <summary>
/// Copies the characters from the source span into the destination, converting each character to lowercase,
/// using the casing rules of the specified culture.
/// </summary>
/// <param name="source">The source span.</param>
/// <param name="destination">The destination span which contains the transformed characters.</param>
/// <param name="culture">An object that supplies culture-specific casing rules.</param>
/// <remarks>If the source and destinations overlap, this method behaves as if the original values are in
/// a temporary location before the destination is overwritten.</remarks>
/// <returns>The number of characters written into the destination span. If the destination is too small, returns -1.</returns>
/// <exception cref="System.ArgumentNullException">
/// Thrown when <paramref name="culture"/> is null.
/// </exception>
public static int ToLower(this ReadOnlySpan <char> source, Span <char> destination, CultureInfo culture)
{
if (culture == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.culture);
}
// Assuming that changing case does not affect length
if (destination.Length < source.Length)
{
return(-1);
}
if (GlobalizationMode.Invariant)
{
TextInfo.ToLowerAsciiInvariant(source, destination);
}
else
{
culture !.TextInfo.ChangeCaseToLower(source, destination); // TODO-NULLABLE: https://github.com/dotnet/csharplang/issues/538
}
return(source.Length);
}
