Link UdfEq and PtrEq to help understand relationship

datafusion/expr/src/ptr_eq.rs

@@ -36,6 +36,8 @@ pub fn arc_ptr_hash<T: ?Sized>(a: &Arc<T>, hasher: &mut impl Hasher) {
 
 /// A wrapper around a pointer that implements `Eq` and `Hash` comparing
 /// the underlying pointer address.
+///
+/// If you have pointers to a `dyn UDF impl` consider using [`super::udf_eq::UdfEq`].
 #[derive(Clone)]
 #[allow(private_bounds)] // This is so that PtrEq can only be used with allowed pointer types (e.g. Arc), without allowing misuse.
 pub struct PtrEq<Ptr: PointerType>(Ptr);

datafusion/expr/src/udf_eq.rs

@@ -23,6 +23,8 @@ use std::sync::Arc;
 
 /// A wrapper around a pointer to UDF that implements `Eq` and `Hash` delegating to
 /// corresponding methods on the UDF trait.
+///
+/// If you want to just compare pointers for equality, use [`super::ptr_eq::PtrEq`].
 #[derive(Clone)]
 #[allow(private_bounds)] // This is so that UdfEq can only be used with allowed pointer types (e.g. Arc), without allowing misuse.
 pub struct UdfEq<Ptr: UdfPointer>(Ptr);