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Add ContiguousMap.CopyKeysTo/CopyValuesTo and obsolete the copying *Span accessors [minor] - #145
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…pan accessors [minor] GetKeysSpan and GetValuesSpan read as zero-copy views, but every call allocated a new array and copied the whole map, so an indexed loop over them was O(n²). CopyKeysTo(Span<TKey>) and CopyValuesTo(Span<TValue>) fill a caller-owned buffer without allocating. The *Span methods keep working, now through those, but are marked [Obsolete] (a warning, not an error) pointing at the replacements and at AsReadOnlySpan() for zero-copy access to Entry.Key/Value. The ContiguousMap span-access benchmark now measures AsReadOnlySpan, the real zero-copy path, instead of the copy. Fixes #102 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017vfJW6AfToAg6F8bcZwwZ5
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Fixes #102
What was wrong
ContiguousMap.GetKeysSpan()andGetValuesSpan()return aReadOnlySpan<T>, and their remarks promised "direct access … from the contiguous memory". In fact every call allocated a new array and copied every entry, sofor (i …) map.GetKeysSpan()[i]was O(n²) and allocated n arrays. Entries are stored asEntry { Key, Value }structs, so a keys-only view can't exist without a copy.Change
This follows the option recommended in the issue's triage comment:
CopyKeysTo(Span<TKey>)andCopyValuesTo(Span<TValue>)fill the start of a caller-owned buffer in insertion order, with no allocation. A destination shorter thanCountthrowsArgumentException(ParamName == "destination") before anything is written.GetKeysSpanandGetValuesSpanare now[Obsolete]as a warning, not an error, so existing callers keep compiling. The message points at the newCopy*Tomethod and atAsReadOnlySpan()for zero-copy access toEntry.Key/Entry.Value. They now delegate toCopy*To, and their remarks state that each call allocates. Removing them would be a[major]change and is left for later.ContiguousMap_SpanAccesswas timing the copy as if it were span access. It now iteratesAsReadOnlySpan().The existing
GetKeysSpan/GetValuesSpantests still run, wrapped in a local#pragma warning disable CS0618.Tests
ContiguousMapTests: insertion-order copies for keys and values, a longer destination keeps its tail, and a shorter destination throws without writing (keys and values).CopyKeysAndValuesTo_DoNotAllocate:GC.GetAllocatedBytesForCurrentThread()shows 0 bytes for both copies.CopyingSpanAccessors_AreObsoleteAndPointAtTheirReplacement: reflection checks the[Obsolete]attribute, its message, and thatIsErroris false.[Obsolete]attributes removed, both cases of the obsolete test fail. Onmain, the new tests don't compile (CS0117, noCopyKeysTo/CopyValuesTo).Containers.Testsuite: 524 passed, 0 failed. The solution builds with no warnings, anddotnet pack(package validation) succeeds.Generated by Claude Code