# Coding conventions

For the most part, we follow the YASGuide. Some key considerations:

• Limit use of Unicode as described in Acceptable Unicode characters.

• Modules and struct names should follow TitleCase convention.

• Function names should be lowercase with words separated by underscores as necessary to improve readability.

• Variable names follow the format used in the ClimateMachine Variable List. In addition, follow CMIP conventions where possible and practicable.

• Document design and purpose rather than mechanics and implementation (document interfaces and embed documentation in code).

• Avoid variable names that coincide with module and struct names, as well as function/variable names that are natively supported.

• Never use the characters l (lowercase letter 'el'), O (uppercase letter 'oh'), or I (uppercase letter 'eye') as single character variable names.

• Try to limit all lines to a maximum of 78 characters.

• import/using should be grouped in the following order:

• Standard library imports.
• Related third party imports.
• Local application/library specific imports.
• Use a blank line between each group of imports.

## Use JuliaFormatter

Once you are happy with your PR, apply our JuliaFormatter.jl settings to all changed files in the repository from the top-level ClimateMachine directory:

julia .dev/climaformat.jl <list of changed files>

This is easiest done by installing our formatting githook.

### Formatting githook

A pre-commit script can be placed in $GIT_DIR/hooks/* which will prevent commits of incorrectly formatted Julia code. It will also provide instructions on how to format the code correctly. Install the script with: $ ln -s ../../.dev/hooks/pre-commit .git/hooks

Then, when you run git commit, an error message will be shown for staged Julia files that are not formatted correctly. For example, if you try to commit changes to src/Arrays/MPIStateArrays.jl that are not formatted correctly:

❯ git commit                                                                                                           │
Activating environment at ~/research/code/ClimateMachine.jl/.dev/Project.toml                                        │
┌ Error: File src/Arrays/MPIStateArrays.jl needs to be indented with:                                                  │
│     julia /home/lucas/research/code/ClimateMachine.jl/.dev/climaformat.jl /home/lucas/research/code/ClimateMachine.jl│
/src/Arrays/MPIStateArrays.jl                                                                                          │
│ and added to the git index via                                                                                       │
└ @ Main ~/research/code/ClimateMachine.jl/.git/hooks/pre-commit:30

Learn more about git hooks.

### Precompiling JuliaFormatter

To speed up the formatter and the githook, a custom system image can be built with the [PackageCompiler]. That said, the following [drawback] from the PackageCompiler repository should be noted:

It should be clearly stated that there are some drawbacks to using a custom sysimage, thereby sidestepping the standard Julia package precompilation system. The biggest drawback is that packages that are compiled into a sysimage (including their dependencies!) are "locked" to the version they where at when the sysimage was created. This means that no matter what package version you have installed in your current project, the one in the sysimage will take precedence. This can lead to bugs where you start with a project that needs a specific version of a package, but you have another one compiled into the sysimage.

There are two helper scripts for doing this. The first will replace your default system image and can be run (from the top-level directory of a clone of ClimateMachine) with

julia .dev/clima_formatter_default_image.jl

If you cannot or do not want to modify the default system image, use the following instead:

julia .dev/clima_formatter_image.jl

which will put the precompile image in .git/hooks/JuliaFormatterSysimage.so. In this case, use the pre-commit.sysimage git hook with:

\$ ln -s ../../.dev/hooks/pre-commit.sysimage .git/hooks/pre-commit
Tip

Putting the system image in .git/hooks protects it from calls to git clean -x.

!!! Note

The script .dev/clima_formatter_image.jl can also take a second arguement with will specify a different path for the system image. If this is used along with the git hook the path in pre-commet.sysimage will need to be updated.

Warning

If you use a system image for the formatter, a new system image must be built in order to update the JuliaFormatter package.