[NotOfficer]

Every CutAfter, CutAfterLast, CutBefore and CutBeforeLast overload that takes a StringComparison and returns a string or writes into a destination ignored the comparison and matched ordinally. Only the span-returning CutSpan*/TryCutSpan* overloads honored it.

"Hello World".CutAfter("WORLD", StringComparison.OrdinalIgnoreCase);
// before: "Hello World"   now: ""

The cause sits in the ReadOnlySpan<char> extension blocks: the StringPool and destination overloads called TryCutSpan*(needle, out cutValue) without passing comparisonType. All other string-returning overloads route through those two.

Culture-sensitive matches

CutAfter and CutAfterLast cut at index + needle.Length. With a culture-sensitive comparison, the matched text can be longer or shorter than the needle. Examples with CutAfter and InvariantCulture:

Value	Needle	Before	Now
"xÅy"	"Å"	"̊y"	"y"
"xÅ"	"Å"	throws ArgumentOutOfRangeException	""
"ab­cd" (soft hyphen)	"bc"	"cd"	"d"

For the four culture comparisons, they now use CompareInfo.IndexOf/LastIndexOf with out int matchLength. Ordinal and OrdinalIgnoreCase keep the MemoryExtensions path. CutBefore and CutBeforeLast only need the start index and were already correct.

Validation

Tests added in StringUtils.ExtTests.cs:

• CutAfter_String_Comparison, CutAfterLast_String_Comparison, CutBefore_String_Comparison, CutBeforeLast_String_Comparison:
  • every overload that takes a StringComparison, for string and span receivers
  • every result shape: string, StringPool, destination (also one char too small), span
  • the needle only matches case-insensitively, so Ordinal has to fail and OrdinalIgnoreCase has to match
• Cut_String_CultureMatchLength: the cases from the table, for all four culture comparisons and all four families.
• Cut_String_CurrentCulture: runs under tr-TR to tell CurrentCulture and InvariantCulture apart.
• Also fixed in the existing tests: the "span for value" sections called CutSpan* on the string instead of .AsSpan() in 8 places.

Checks run locally on Windows with SDK 11.0.100:

• dotnet test -c Release: 108 passed on net10.0 and net11.0, 0 build warnings.
• The new tests against the old code (in a worktree of master): all 9 fail on both target frameworks.

The culture tests need ICU, which ubuntu-latest has. They would fail with InvariantGlobalization=true.

🤖 Generated by Opus 5.5 (xhigh) with Claude Code in T3 Code