#array #struct #derive #field #iter

macro arraygen-docfix

Derive macro for generating arrays from struct fields

2 releases

0.1.8 Nov 25, 2019
0.1.7 Nov 25, 2019

#27 in #iter

MIT license

377 lines


Crates.io Docs

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 {
    first_name: String,
    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();

    format!("{:?}", person),
    "Person { first_name: \"ada\", last_name: \"lovelace\" }"
// Notice how it was not lowercased on type definition
// but now it is.

As you can see above, the gen_array attribute generates a new method returning an array of the indicated type. And the in_array attribute tells which fields are contained within the array returned by that method.

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

impl Person {
    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 and the return type.

#[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 include.

// inside a struct
name: String,

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.


For more information, check the documentation page.


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 Proposals to give your opinion on this matter.


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. That's why I decided to work on this new solution.




~31K SLoC