Is there a way to get the field names of a struct in a macro?

by

A macro is expanded during parsing, more or less; it has no access to the AST or anything like that—all it has access to is the stuff that you pass to it, which for my_macro!(S) is purely that there should be a type named S.

If you define the struct as part of the macro then you can know about the fields:

macro_rules! my_macro {
    (struct $name:ident {
        $($field_name:ident: $field_type:ty,)*
    }) => {
        struct $name {
            $($field_name: $field_type,)*
        }

        impl $name {
            // This is purely an example—not a good one.
            fn get_field_names() -> Vec<&'static str> {
                vec![$(stringify!($field_name)),*]
            }
        }
    }
}

my_macro! {
    struct S {
        a: String,
        b: String,
    }
}

// S::get_field_names() == vec!["a", "b"]

… but this is, while potentially useful, often going to be a dubious thing to do.

More Related Contents:

  1. Why can’t I store a value and a reference to that value in the same struct?
  2. The compiler suggests I add a ‘static lifetime because the parameter type may not live long enough, but I don’t think that’s what I want
  3. How do I pass disjoint slices from a vector to different threads?
  4. Why does Iterator::take_while take ownership of the iterator?
  5. When should I implement std::convert::From vs std::convert::Into?
  6. How can I call a mutating method while holding a reference to self?
  7. How do you actually use dynamically sized types in Rust?
  8. How do I use the Entry API with an expensive key that is only constructed if the Entry is Vacant?
  9. “parameter `’a` is never used” error when ‘a is used in type parameter bound
  10. Borrowing references to attributes in a struct
  11. How do I split a string in Rust?
  12. Is it possible to implement methods on type aliases?
  13. How can I use a module from outside the src folder in a binary project, such as for integration tests or benchmarks?
  14. How to match on data type in Rust?
  15. Why does Rust allow mutation through a reference field using an immutable binding?
  16. How can I modify self in a closure called from a member function?
  17. How do I move out of a struct field that is an Option?
  18. How can I change enum variant while moving the field to the new variant?
  19. What is unwrap in Rust, and what is it used for?
  20. HashMap borrow issue when trying to implement find or insert
  21. How can I find a subsequence in a &[u8] slice?
  22. Why “explicit lifetime bound required” for Box in struct?
  23. How to print a Vec?
  24. Why should I prefer `Option::ok_or_else` instead of `Option::ok_or`?
  25. How to get an Option’s value or set it if it’s empty?
  26. How to set a field in a struct with an empty value?
  27. Is the resource of a shadowed variable binding freed immediately?
  28. How can I download Rust API docs?
  29. How can I convert a hex string to a u8 slice?
  30. How do I pin indirect dependencies of a crate?

Leave a Comment