Function mx_query 

pub unsafe fn mx_query(sexp: SEXP, tag: mx_tag) -> *const c_void

Query an object for an interface vtable by tag.

Looks up whether the object implements the trait identified by tag, and returns a pointer to the vtable if so.

Arguments

• sexp - R external pointer wrapping an erased object
• tag - Tag identifying the requested trait interface

Returns

• Non-null pointer to the trait’s vtable if implemented
• Null pointer if:
  • sexp is not a valid erased object
  • The object does not implement the requested trait

Safety

• sexp must be a valid SEXP
• Must be called on R’s main thread
• The returned pointer must be cast to the correct vtable type

Example

let vtable = unsafe { mx_query(obj, TAG_FOO) };
if !vtable.is_null() {
    let foo_vtable = vtable.cast::<FooVTable>();
    // Call method through vtable...
}