Caveats

Explicit interface members

The DLR cannot see members implemented explicitly on an interface. Neither can ?, Dyn.get, or C# dynamic. If you need that member, call it through the interface type in ordinary F#.

Conversion vs missing

RuntimeBinderException means the binder could not do what you asked. That is not always "the member is missing":

• Missing property → binder exception → tryGet returns None
• Present property, wrong 'T → conversion / unbox failure → throws, tryGet does not swallow it
• Void method inferred as a value → binder exception

Annotate 'T / unit so the binder and the conversion agree.

A present null exists

Dyn.exists "x" is true if InvokeGet succeeded, including when the value is null. tryGet returns Some null for a reference type. That is different from missing.

Function-typed results delay the call

If F# infers 'TResult as a function, ? / Dyn.get / Dyn.invokeMember return a callable. A missing member in that mode used to look like Some (fun …) until you applied it. tryGet does InvokeGet first, so a missing member is None even when 'T is a function.

Explicit interface and COM

COM and IDynamicMetaObjectProvider objects can succeed on names that reflection does not list. Existence checks go through InvokeGet, not GetMemberNames.

Trimming and NativeAOT

This library is DLR-based. It is not trim-safe or NativeAOT-safe. Members it resolves at runtime can be removed by the trimmer. Do not publish a trimmed consumer and expect ? to keep working.

Historical .NET Core 2.0.0–2.0.2 bug

Nested classes inside generic classes broke C# dynamic (substring argument-length exceptions). .NET Core 2.0.3+ and every current TFM this package ships are fine. Recorded as #11.

Security

Member names are capabilities. Do not build ? / Dyn.get / Dyn.invokeMember names from untrusted input. See SECURITY.md.