recursive equal, and firstDifference functions

[Jonathan M Davis]

On Tuesday, March 19, 2013 22:43:10 Dan wrote:
> The above works with the built-in AAs.
> Please offer an example.

It works because the outer type defines toHash. Without toHash, the built-in 
AAs won't work. If you're dealing with member variables which don't have 
toHash, then doing something like you did is an option, but the outer type 
still needs toHash, and if any of the member variables define an opEquals but 
not a toHash, then you risk having your hash change when a member variable 
changes even when the new value of the member variable is considered equal to 
the old one (e.g. because a cached value or some other member variable in that 
type is not considered to be part of the equality of an object but _would_ be 
considered to be part of the hash if you use reflection to generate a hash from 
all of that type's member variables). So, using reflection to generate hashes 
for arbitrary types can be risky. Whether it works on not depends on how those 
types are defined and what you're doing with them.

But the main problem that I'm pointing out is that you can't define your own, 
non-standard functions for equality or hashing or whatever and expect your 
types to play nicely with other stuff. If your stuff is wrapped in types that do 
define the proper functions for that (like in your example), then it can work, 
but the types which were wrapped won't play nice outside of the wrapper.

- Jonathan M Davis