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I really like this about Rust, implementing equality is just another trait. The same is true of comparison operators. If you don’t want a type to be able to be

I really like this about Rust, implementing equality is just another trait. The same is true of comparison operators. If you don’t want a type to be able to be compared by == you can make it always evaluate to false or even panic and give a message that the type cannot be used in that way. That might aggravate coders who do not test comprehensively but it is an option. Edit: This is a response to the concerns of the article. For general info on this it’s a great introduction to Rust’s awesome documentation. https://doc.rust-lang.org/std/cmp/trait.Eq.html https://doc.rust-lang.org/std/cmp/trait.Eq.html

tus88 7y ago
You mean there is no compile time way to accomplish that? Doesn't sound very Rust-like.
- jeffadotio 7y ago
  “Option” is the operative word. A type that does not implement the correct trait cannot be used in a way that requires the trait. If you are writing anything non-trivial that would probably be preferable. It requires nothing, that is the default behavior, so I did not bother to mention it.
- re 7y ago
  It is determined at compile time; I'm not sure why GP is suggesting returning false if you don't want types to be compared. By default structs are not comparable. If you opt-in to the standard PartialEq implementation using the `derive` annotation[1], it will only allow a struct to be compared for equality with other structs of the same type. You can choose to add implementations to compare against other types[2]. [1] https://doc.rust-lang.org/book/ch05-02-example-structs.html#adding-useful-functionality-with-derived-traits https://doc.rust-lang.org/book/ch05-02-example-structs.html#... [2] https://doc.rust-lang.org/std/cmp/trait.PartialEq.html#how-can-i-compare-two-different-types https://doc.rust-lang.org/std/cmp/trait.PartialEq.html#how-c...
  - artursapek 7y ago
    Rust is such a delightful language.
- aliceryhl 7y ago
  I don't know why they would make it always return false. In Rust you can just not implement Eq for the type, and it becomes a compile error to try and compare it.

tus88 7y ago

You mean there is no compile time way to accomplish that? Doesn't sound very Rust-like.

jeffadotio 7y ago
“Option” is the operative word. A type that does not implement the correct trait cannot be used in a way that requires the trait. If you are writing anything non-trivial that would probably be preferable. It requires nothing, that is the default behavior, so I did not bother to mention it.
re 7y ago
It is determined at compile time; I'm not sure why GP is suggesting returning false if you don't want types to be compared. By default structs are not comparable. If you opt-in to the standard PartialEq implementation using the `derive` annotation[1], it will only allow a struct to be compared for equality with other structs of the same type. You can choose to add implementations to compare against other types[2]. [1] https://doc.rust-lang.org/book/ch05-02-example-structs.html#adding-useful-functionality-with-derived-traits https://doc.rust-lang.org/book/ch05-02-example-structs.html#... [2] https://doc.rust-lang.org/std/cmp/trait.PartialEq.html#how-can-i-compare-two-different-types https://doc.rust-lang.org/std/cmp/trait.PartialEq.html#how-c...
- artursapek 7y ago
  Rust is such a delightful language.
aliceryhl 7y ago
I don't know why they would make it always return false. In Rust you can just not implement Eq for the type, and it becomes a compile error to try and compare it.