CODEWITHSUNDEEP
rust
yegor256
yegor256

Reputation: 105043

How to break a large Rust impl block into files?

Here is what I have in foo.rs:

pub struct Foo {
  // a few attributes
}

impl Foo {
  // 20+ public functions 
}
// 100+ tests

The file is too long (2000+ lines of code). How can I break it into files without changing the structure of the code: I want to still have one struct Foo with many functions and many unit tests.

Upvotes: 1

Views: 730

Answers (2)

Jonathan Giddy
Jonathan Giddy

Reputation: 1801

It appears that the tests make up a large portion of the file. If you have followed the usual pattern of having tests in a submodule (mod tests) then the simplest way to break up this file is to move the tests module to a separate file.

You can either:

  • create a directory foo containing mod.rs with the non-test code and tests.rs with the contents of the tests sub-module, or
  • keep foo.rs with the non-test code and create a directory foo only containing the tests.rs file.
// Keep this in foo.rs or move to foo/mod.rs
pub struct Foo {
  // a few attributes
}

impl Foo {
  // 20+ public functions 
}

// Replace this module with `mod tests;`
mod tests {
    // move the contents to a new file `foo/tests.rs`
    // 100+ tests
}

Upvotes: 4

at54321
at54321

Reputation: 11698

Rust allows you to have impl blocks in separate files. So you can have, for example:

In file1.rs:

pub struct Foo {
    // a few attributes
}

In file2.rs:

impl Foo {
    // some methods
}

In file3.rs:

impl Abc for Foo {
    // other methods
}

In file4.rs:

impl Xyz for Foo {
    // other methods
}

It's also worth mentioning that if you have private fields in your struct Foo (the default, i.e. you don't add pub or any other visibility modifiers to your fields) , you can still access them in other files, but there is a restriction: they can only be accessed by the current module and its descendants.

Upvotes: 3

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