Fix IReadOnlyDictionary DeepClone throwing InvalidCastException - #78
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The read-only dictionary overload passed the DeepClone method group to ToDictionary, which bound it to KeyValuePair and built a dictionary keyed by pairs, so the cast back to IReadOnlyDictionary failed on every call. Clone keys and values individually, as the IDictionary overload does, and add the missing null guard. Fixes #76 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Q8KgDr8CfZLWPQ5o6nZdcV
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This was referenced Sep 28, 2026
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Fixes #76
What was wrong
DeepClone(this IReadOnlyDictionary<TKey, TValue>)passed theDeepClonemethod group toToDictionary. That bound it toDeepClone<KeyValuePair<TKey, TValue>>, so the method built a dictionary keyed by pairs. The cast back toIReadOnlyDictionary<TKey, TValue>then threwInvalidCastExceptionon every call, including on an empty dictionary.Change
IDictionaryoverload does.Ensure.NotNull(source)guard and documents theArgumentNullException.Tests
SpecializedCollectionTestsgains three tests:ReadOnlyDictionary_DeepClone_ShouldCreateIndependentCopychecks that values are independentIDeepCloneablecopies.ReadOnlyDictionary_DeepClone_Empty_ShouldReturnEmptyDictionaryReadOnlyDictionary_DeepClone_Null_ShouldThrowI checked the tests against the old code. With the fix reverted, the first two fail with the
InvalidCastExceptionfrom the issue. With the fix in place, the full suite passes, 36 of 36, on net10.0.Issue #77 also asks to keep the comparer and remove the ambiguity with
Dictionary<,>. This PR deliberately leaves that out.🤖 Generated with Claude Code
https://claude.ai/code/session_01Q8KgDr8CfZLWPQ5o6nZdcV
Generated by Claude Code