Add Unchecked.withNull for unconstrained C# nullable-generic interop - #20232
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Add Unchecked.withNull for unconstrained C# nullable-generic interop#20232T-Gro wants to merge 2 commits into
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Adds an inline escape hatch re-typing 'T to 'T | null with no not null / not struct constraint, so unconstrained C# nullable-generic APIs (T? M<T>()) can be implemented and consumed from F#. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: acdc940e-b98f-4072-b143-a3e296e12fcb
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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: acdc940e-b98f-4072-b143-a3e296e12fcb
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Relates to #17734.
Adds
Unchecked.withNull : 'T -> 'T | null, an escape hatch for implementing and consuming unconstrained C# nullable-generic APIs (T? M<T>(),interface { T? GetValue<T>(int) }). UnlikeOperators.withNullit places nonot null/not structconstraint on'T, so such a slot can be satisfied without FS3261.It is
inlineand erases to a retype ((# "" value : 'T | null #)) — nothing lands in IL. Documented as unsafe/interop-only:'T | nullis meaningless for a struct'T. Assigningnullto a resulting mutable at a struct lowers todefault(T)(ILVerify-clean through multiple generic layers); the same on a concrete struct mutable stays a compile error (FS0043).