Fix string-left relational operator binding for custom types#376
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israellot wants to merge 5 commits into
Open
Fix string-left relational operator binding for custom types#376israellot wants to merge 5 commits into
israellot wants to merge 5 commits into
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generalize default expressions for generic methods
davideicardi
approved these changes
Jun 4, 2026
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Summary
Fixes string-left relational operator binding for custom types, e.g. "10" < m, "10" <= m, "10" > m, and "10" >= m.
Root cause
Relational operators special-cased any comparison with a string left operand and routed it through string.Compare. For string vs custom type, no matching string.Compare(string, T) exists, so a null MethodInfo was passed to Expression.Call, causing ArgumentNullException.
Fix
• Use the string.Compare shortcut only for string/string comparisons.
• Let string/custom relationals use normal binary operator resolution.
• Add fallback binding through a single implicit conversion when no direct user-defined operator matches.
Tests
Added NUnit coverage for all four relational operators in both operand orders, including direct string/custom operators, implicit-conversion fallback, and equality regressions.