Arraygen

This crate provides Arraygen derive macro for structs, which generates methods returning arrays filled with the selected struct fields.

Complete example:

#[derive(Arraygen, Debug)]
#[gen_array(fn get_names: &mut String)]
struct Person {
    #[in_array(get_names)]
    first_name: String,
    #[in_array(get_names)]
    last_name: String,
}

let mut person = Person { first_name: "Ada".into(), last_name: "Lovelace".into() };
for name in person.get_names().iter_mut() {
    **name = name.to_lowercase();
}

assert_eq!(format!("{:?}", person), "Person { first_name: \"ada\", last_name: \"lovelace\" }"); // PASSES !

As you can see above, the attribute gen_array generates a new method returning an array of the given type. And the attribute in_array selects those struct fields to be used by that method.

What Arraygen does under the hood is simmply generating the following impl:

impl Person {
    #[inline(always)]
    fn get_names(&mut self) -> [&mut String; 2] {
        [&mut self.first_name, &mut self.last_name]
    }
}

The attribute gen_array

For generating an Arraygen method you have to use the attribute gen_array on top of the struct, indicating the method name.

#[derive(Arraygen)]
#[gen_array(fn get_strings: &String]
struct Foo {...}

In the code above, the struct Foo would have a new method with the following signature: fn get_strings(&self) -> [&Strings; ?] {...}.

The attribute in_array

In order to fill your Arraygen methods with struct fields, you have to use the attribute in_array in each struct field you want to select.

// inside a struct
#[in_array(get_strings)]
name: String

#[in_array(get_strings)]
id: String

You have to match the method name used in gen_array and in in_array in order to include those fields in the generated method.

Documentation

For more information, check the documentation page.

Limitations

There are not particular limitations, really. You can use this derive to return Copy objects, Trait objects, and basically any kind of object that can be a struct member.

Also, notice that there are no dynamic memory allocations involved.

The only drawback would be a little impact in compilation times.

About the Syntax

I'm open to change the syntax for the 1.0 version. Participate in the issue Syntax propolsas to give your opinion on this matter.

GettersByType

This crate is heavily inspired by GettersByType which is another derive that allows you to do the same thing. But that one is more opinionated, less flexible and less powerful, with the only advantage of being less verbose.

License

MIT