style-guide.md

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---
layout: style-guide title: Rust Style Guide category: style-guide tags: [style-guide,contributing]
---

Rust style guide.

All of the codebase should be formatted by the rustfmt. However, the code style is way more than just formatting. In many cases formatting can be automated. According to rustfmt docs: “formatting code is a mostly mechanical task which takes both time and mental effort. By using an automatic formatting tool, a programmer is relieved of this task and can concentrate on more important things.”. While in many cases it is true, if the code author does not take extra effort to make his code pretty by refactoring long lines to variables, moving code to specific modules, or sections, the formatting tool will result in code that is hard to read and hard to write. Thus, it is important to take time to write code in such way that we can be proud of its quality. The following document provides you with a detailed guide regarding the code quality we are looking for.

Code formatting in macros.

Unfortunately, rustfmt is not working inside of macros. Thus, this code should be manually formatted in the same was as rustfmt would do it.

Submodules and imports.

• Design your files to be imported as module.
  Design names of your libraries, structs, and functions to be imported as modules. For example, prefer an import use graph; and it's usage graph::Node::new() over use graph::new_node. This design minimizes the amount of imports and allows related modules to import shorter names to the scope.

• Don't use relative imports.
  Do not use super:: nor self:: imports in files (you can use them in localy defined modules). Use absolute imports or imports from local submodules only.

• Use Enso Formatter to format your imports
  Run the build/enso-formatter script (e.g. by running cargo run -p enso-formatter) to format imports in all files before contributing your PR.

Sections.

Source files should be divided into sections. Section headers should be placed before each new "concept" defined in a file. By "concept" we normally mean a structure with related implementations. In case related implementations use some helper structs with very small implementations, these helper structs may be defined in the same section. Moreover, the code in each section should be divided into sub-sections, grouping related definitions. At least one section should be defined in a file (if there is at least one struct definition as well). For example:

// =================
// === AxisOrder ===
// =================

/// Defines the order in which particular axis coordinates are processed. Used
/// for example to define the rotation order in `DisplayObject`.
pub enum AxisOrder { XYZ, XZY, YXZ, YZX, ZXY, ZYX }

impl Default for AxisOrder {
    fn default() -> Self { Self::XYZ }
}


// =================
// === Transform ===
// =================

/// Defines the order in which transformations (scale, rotate, translate) are
/// applied to a particular object.
pub enum TransformOrder {
    ScaleRotateTranslate,
    ScaleTranslateRotate,
    RotateScaleTranslate,
    RotateTranslateScale,
    TranslateRotateScale,
    TranslateScaleRotate
}

impl Default for TransformOrder {
    fn default() -> Self { Self::ScaleRotateTranslate }
}


// =============================
// === HierarchicalTransform ===
// =============================

pub struct HierarchicalTransform<OnChange> {
    transform: Transform,
    transform_matrix: Matrix4<f32>,
    origin: Matrix4<f32>,
    matrix: Matrix4<f32>,
    pub dirty: dirty::SharedBool<OnChange>,
    pub logger: Logger,
}

impl<OnChange> HierarchicalTransform<OnChange> {
    pub fn new(logger: Logger, on_change: OnChange) -> Self {
        let logger_dirty = logger.sub("dirty");
        let transform = default();
        let transform_matrix = Matrix4::identity();
        let origin = Matrix4::identity();
        let matrix = Matrix4::identity();
        let dirty = dirty::SharedBool::new(logger_dirty, on_change);
        Self { transform, transform_matrix, origin, matrix, dirty, logger }
    }
}


// === Getters ===

impl<OnChange> HierarchicalTransform<OnChange> {
    pub fn position(&self) -> &Vector3<f32> {
        &self.transform.position
    }

    pub fn rotation(&self) -> &Vector3<f32> {
        &self.transform.rotation
    }

    ...
}


// === Setters ===

impl<OnChange: Callback0> HierarchicalTransform<OnChange> {
    pub fn position_mut(&mut self) -> &mut Vector3<f32> {
        self.dirty.set();
        &mut self.transform.position
    }

    pub fn rotation_mut(&mut self) -> &mut Vector3<f32> {
        self.dirty.set();
        &mut self.transform.rotation
    }

    ...
}

Multiline Expressions

Most (preferably all) expressions should be single line. Multiline expressions are hard to read and introduce noise in the code. Often, it is also an indicator of code that is not properly refactored. Try to refactor parts of multiline expressions to well-named variables, and divide them to several single-line expressions.

Example of poorly formatted code:

pub fn new() -> Self {
    let shape_dirty = ShapeDirty::new(logger.sub("shape_dirty"),
                                      on_dirty.clone());
    let dirty_flag = MeshRegistryDirty::new(logger.sub("mesh_registry_dirty"),
                                            on_dirty);
    Self { dirty_flag, dirty_flag }
}

Example of properly formatted code:

pub fn new() -> Self {
    let sub_logger = logger.sub("shape_dirty");
    let shape_dirty = ShapeDirty::new(sub_logger, on_dirty.clone());
    let sub_logger = logger.sub("mesh_registry_dirty");
    let dirty_flag = MeshRegistryDirty::new(sub_logger, on_dirty);
    Self { shape_dirty, dirty_flag }
}

Getters and Setters

Getters do not have the get_ prefix, while setters do. If a setter is provided (method with the set_ prefix), a mut accessor should be provided as well. The correct way of defining getters and setters is presented below:

fn field(&self) -> &Type {
    &self.field
}

fn field_mut(&mut self) -> &mut Type {
    &mut self.field
}

fn set_field(&mut self, val: Type) {
    *self.field_mut = val;
}

Trait exporting

All names should be designed to be used in a qualified fashion. However, this makes one situation tricky. In order to use methods defined in a trait, it has to be in scope. Consider a trait display::Object. We want to use it as function bound like fn test<T:display::Object>(t:T) {...}, and we also want to use methods defined in this trait (so it has to be in scope). In such a case, Clippy warns that display::Object is unnecessary qualification and could be replaced simply by Object, which is not what we want. Thus, in order to export traits, please always rename them using the following convention:

/// Common traits.
pub mod traits {
    // Read the Rust Style Guide to learn more about the used naming.
    pub use super::Object    as TRAIT_Object;
    pub use super::ObjectOps as TRAIT_ObjectOps;
}

Having such a definition, we can import traits to scope using use display::object::traits::*, and we would not have any warning about unnecessary qualification anymore.