Look for places to collapse AsSpan().Slice(start, length) into .AsSpan(start,length)

[ghost]

No description provided.

[tarekgh]

@atsushikan do we still have work to do here? or this is done?

[ghost]

Work hasn't started on this. (BTW, this work is cleanup and microoptimization rather than "Enhancement.")

[stephentoub]

A quick search in corefx shows this:

  D:\repos\corefx\src\Common\src\CoreLib\System\String.Manipulation.cs(1139):                    this.AsSpan().Slice(thisIdx, count).CopyTo(dstSpan.Slice(dstIdx));
  D:\repos\corefx\src\Common\src\CoreLib\System\String.Manipulation.cs(1151):            this.AsSpan().Slice(thisIdx).CopyTo(dstSpan.Slice(dstIdx));
  D:\repos\corefx\src\Common\src\CoreLib\System\TimeZoneInfo.Unix.cs(1201):                        if (int.TryParse(dateRule.AsSpan().Slice(1, firstDotIndex - 1), out month) &&
  D:\repos\corefx\src\Common\src\CoreLib\System\TimeZoneInfo.Unix.cs(1202):                            int.TryParse(dateRule.AsSpan().Slice(firstDotIndex + 1, secondDotIndex - firstDotIndex - 1), out week) &&
  D:\repos\corefx\src\Common\src\CoreLib\System\TimeZoneInfo.Unix.cs(1203):                            int.TryParse(dateRule.AsSpan().Slice(secondDotIndex + 1), out int day))
  D:\repos\corefx\src\Common\src\CoreLib\System\Globalization\CompareInfo.cs(509):                string1.AsSpan().Slice(offset1, length1),
  D:\repos\corefx\src\Common\src\CoreLib\System\Globalization\CompareInfo.cs(510):                string2.AsSpan().Slice(offset2, length2),
  D:\repos\corefx\src\Common\src\CoreLib\System\Globalization\CompareInfo.cs(534):            return CompareOrdinalIgnoreCase(strA.AsSpan().Slice(indexA, lengthA), strB.AsSpan().Slice(indexB, lengthB));
  D:\repos\corefx\src\Common\src\CoreLib\System\Globalization\DateTimeParse.cs(5048):                        if (m_info.CompareOptionIgnoreCase(Value.Slice(thisPosition, segmentLength), target.AsSpan().Slice(targetPosition, segmentLength)) != 0)
  D:\repos\corefx\src\Common\src\CoreLib\System\Globalization\DateTimeParse.cs(5074):                    if (m_info.CompareOptionIgnoreCase(Value.Slice(thisPosition, segmentLength), target.AsSpan().Slice(targetPosition, segmentLength)) != 0)
  D:\repos\corefx\src\Common\src\CoreLib\System\Globalization\HijriCalendar.Win32.cs(72):                                int advance = Int32.Parse(str.AsSpan().Slice(HijriAdvanceRegKeyEntry.Length), provider:CultureInfo.InvariantCulture);
  D:\repos\corefx\src\Common\src\CoreLib\System\IO\Path.Windows.cs(86):                combinedPath = Join(GetPathRoot(basePath.AsSpan()), path.AsSpan().Slice(1)); // Cut the separator to ensure we don't end up with two separators when joining with the root.
  D:\repos\corefx\src\Common\src\CoreLib\System\IO\Path.Windows.cs(98):                    combinedPath = Join(basePath, path.AsSpan().Slice(2));
  D:\repos\corefx\src\Common\src\CoreLib\System\IO\Path.Windows.cs(108):                            ? JoinInternal(basePath.AsSpan().Slice(0, 4), path, @"\")
  D:\repos\corefx\src\Common\src\CoreLib\System\IO\Path.Windows.cs(109):                            : JoinInternal(basePath.AsSpan().Slice(0, 4), path.AsSpan().Slice(0, 2), @"\", path.AsSpan().Slice(2));
  D:\repos\corefx\src\Common\src\CoreLib\System\IO\PathHelper.Windows.cs(87):                buffer.Append(content.AsSpan().Slice(PathInternal.UncPrefixLength));
  D:\repos\corefx\src\Common\src\CoreLib\System\IO\PathHelper.Windows.cs(201):                        outputBuilder.Append(inputBuilder.AsSpan().Slice(foundIndex, inputBuilder.Length - foundIndex));
  D:\repos\corefx\src\Common\src\CoreLib\System\IO\PathHelper.Windows.cs(221):            ReadOnlySpan<char> output = builderToUse.AsSpan().Slice(rootDifference);
  D:\repos\corefx\src\Common\src\CoreLib\System\Text\StringBuilder.cs(1555):                            itemFormatSpan = format.AsSpan().Slice(startPos, pos - startPos);
  D:\repos\corefx\src\Common\src\Interop\Unix\System.Security.Cryptography.Native\Interop.OpenSslVersion.cs(26):                    if (!Version.TryParse(OpenSslVersionDescription().AsSpan().Slice(OpenSSL.Length, 5).ToString(), out s_opensslVersion))
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\Asn1V2.Serializer.cs(638):                        valAsMemory.Span.CopyTo(tooBig.AsSpan().Slice(1));
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\Asn1V2.Serializer.cs(884):                                return new ReadOnlyMemory<byte>(rented.AsSpan().Slice(0, bytesWritten).ToArray());
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\Asn1V2.Serializer.cs(915):                                return new ReadOnlyMemory<byte>(rented.AsSpan().Slice(0, bytesWritten).ToArray());
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(102):            if (!tag.TryWrite(_buffer.AsSpan().Slice(_offset, spaceRequired), out int written) ||
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(193):            preEncodedValue.Span.CopyTo(_buffer.AsSpan().Slice(_offset));
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(452):            bitString.CopyTo(_buffer.AsSpan().Slice(_offset));
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(511):                dest = _buffer.AsSpan().Slice(_offset);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(524):            dest = _buffer.AsSpan().Slice(_offset);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(658):            octetString.CopyTo(_buffer.AsSpan().Slice(_offset));
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(710):                dest = _buffer.AsSpan().Slice(_offset);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(719):            dest = _buffer.AsSpan().Slice(_offset);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(846):                int localLen = EncodeSubIdentifier(tmp.AsSpan().Slice(tmpOffset), ref subIdentifier);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(852):                    localLen = EncodeSubIdentifier(tmp.AsSpan().Slice(tmpOffset), ref subIdentifier);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(1124):            Span<byte> baseSpan = _buffer.AsSpan().Slice(_offset);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(1237):            Span<byte> baseSpan = _buffer.AsSpan().Slice(_offset);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(1290):            _buffer.AsSpan().Slice(0, _offset).CopyTo(dest);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(1308):            return _buffer.AsSpan().Slice(0, _offset).ToArray();
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(1475):                    Span<byte> dest = _buffer.AsSpan().Slice(_offset, size);
  D:\repos\corefx\src\Common\src\System\Security\Cryptography\AsnWriter.cs(1520):            WriteConstructedCerOctetString(tag, tmp.AsSpan().Slice(0, size));
  D:\repos\corefx\src\System.Diagnostics.Process\src\System\Diagnostics\Process.Linux.cs(91):                    Double.TryParse(text.AsSpan().Slice(0, length), NumberStyles.AllowDecimalPoint, NumberFormatInfo.InvariantInfo, out uptimeSeconds);
  D:\repos\corefx\src\System.Private.Xml\src\System\Xml\NameTable.cs(243):            ReadOnlySpan<byte> bytes = key.AsSpan().Slice(start, len).AsBytes();
  D:\repos\corefx\src\System.Runtime.Extensions\src\System\IO\StringReader.cs(141):                _s.AsSpan().Slice(_pos, n).CopyTo(buffer);

[tarekgh]

Work hasn't started on this. (BTW, this work is cleanup and microoptimization rather than "Enhancement.")

that is what meant by "Enhancement".

@stephentoub you marked it as up-for-grabs so we should un-assign @atsushikan if you think someone else will pick it up.

[stephentoub]

so we should un-assign

Not necessary unless he wants that. This is just the kind of thing that anyone can do; doesn't require Ati's skill set.

[tarekgh]

what I meant, people usually don't pick the assigned issues. anyway, I'll see if I can do this one myself.

[khellang]

What about shipping an analyzer and code fix for this?

[ahsonkhan]

@tarekgh, can you please fix such uses in coreclr as well?

For instance (the only one I could find): https://github.com/dotnet/coreclr/blob/76be5e3928cbfa01e96086e532a6476f1acac293/src/mscorlib/shared/System/IO/PathInternal.cs#L137

[ahsonkhan]

What about shipping an analyzer and code fix for this?

See dotnet/corefxlab#2206 (experimental, trying it out)