[DougBTX]

Even with the hash set solution, it would be nice to not copy the string contents, which unfortunately is needed if the hash set contains lowercased versions of the strings. On the other hand, converting all strings to lowercase then comparing them isn't a great way to case-insensitively compare strings anyway, as Unicode doesn't guarantee that will work.

The UniCase crate defines a wrapper around strings with a case-insensitive Eq implementation, so this works:

    use std::collections::HashSet;
    use unicase::UniCase;

    fn main () {
        let strings = vec![
            "apple", "cAt", "cat", "Dog", "apple", "dog", "Cat",
            "Apple", "dOg", "banana", "cat", "dog", "apple",
        ];
        
        let mut set = HashSet::new();
        
        let strings: Vec<_> = strings
            .iter()
            .filter(|&string| set.insert(UniCase::new(string)))
            .collect();
        
        println!("{:?}", strings);
    }

https://play.rust-lang.org/?version=stable&mode=debug&editio...

[nicoburns]

This is pretty cool. People might think it's cheating to pull in a crate. But IMO the fact that its super easy to pull in a crate in Rust is one of the best things about the language.