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> fn greet(req: HttpRequest) -> impl Responder Nice to see front page example using 'impl', the recent most improvement in ergonomics. Before 1.26 things would

• rkangel 8y ago
  To explain this to people who don't know the background - this is about 'impl NameOfTrait' in the return position. It allows functions to return an object that provides a certain interface without specifying the actual type of that object. This was only previously true by wrapping it in a 'box', which meant a heap allocation and dynamic dispatch. The 'impl trait' provides static dispatch and no other overhead, so produces equivalent code to returning the type directly, but with all the abstraction flexibility that you want.
  • ejanus 8y ago
    What is the use case ? Is there simple examples one could go through?
    • iopq 8y ago
      Usually you return a closure with impl Fn. Another use case is to return an iterator. I wrote a post about it. Let me know if it helps. https://medium.com/@iopguy/impl-trait-in-rust-explanation-efde0d94946a https://medium.com/@iopguy/impl-trait-in-rust-explanation-ef...
      • ejanus 8y ago
        Your code is nothing but Magic . I have spent time trying to wrap my head around it. I am almost there but I don't understand .map(<&str>::into) . Monoid implements String
        • ejanus 8y ago
          Finally, that code is itched in my brain
    • steveklabnik 8y ago
      https://blog.rust-lang.org/2018/05/10/Rust-1.26.html https://blog.rust-lang.org/2018/05/10/Rust-1.26.html has a section about it.
      • ejanus 8y ago
        Thanks