this post was submitted on 15 Nov 2024
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i've only read about rust, but is there a way to influence those automatic implementations?
equality for example could be that somethings literally point to the same thing in memory, or it could be that two structs have only values that are equal to each other
Not for the built-in Eq derive macro. But you can write your own derive macros that do allow you to take options, yeah.
Equality in rust is value equality per default, that's what these traits are for. If you want to check pointer equality you'd use the
std::ptr::eqfunction to check if two pointers are equal, which is rather rare in practice. You can also implement thePartialEqtrait yourself if you need custom equality checks.I worked on software at one point that had at it's core a number of "modes" that it switched between. It was, at the time, in the process of migrating from enums and switch/case trees to an inheritance based system.
In practice this meant there was a single instance of "Mode" for each mode which used pointer equality to switch/case on modes like an enum.
To add a new mode (that did nothing) I think I had to change about 6 different places.
Not really related to the pointer thing, but Rust also has pattern matching based on Enums, as they're actually sum-types and not just numbers