Julia Package Extensions

Build package extensions (weak dependencies) to provide optional functionality that loads only when users import the trigger package(s).

Why Extensions?

1. •Minimal base package: Users who don't need plotting don't pay for Makie compilation
2. •Clean dependencies: Heavy packages stay optional
3. •Precompilation benefits: Extensions precompile separately
4. •Type piracy prevention: Methods involving external types live in extensions

Tradeoff: Extensions add complexity. Use them when the trigger dependency is heavy (plotting, GPU, optimization solvers) or when the functionality is truly optional.

Project.toml Configuration

[weakdeps]
Makie = "ee78f7c6-11fb-53f2-987a-cfe4a2b5a57a"
CUDA = "052768ef-5323-5732-b1bb-66c8b64840ba"

[extensions]
MyPackageMakieExt = "Makie"
MyPackageCUDAExt = "CUDA"
# Multiple triggers (loads when ALL are imported)
MyPackageOscarExt = ["Hecke", "Oscar"]

[compat]
Makie = "0.20, 0.21, 0.22, 0.23, 0.24"

File Structure

MyPackage.jl/
├── Project.toml
├── src/
│   └── MyPackage.jl
└── ext/
    ├── MyPackageMakieExt/
    │   ├── MyPackageMakieExt.jl
    │   └── recipes.jl
    └── MyPackageCUDAExt.jl

Naming convention: {PackageName}{TriggerDep}Ext

Extension Module Structure

# ext/MyPackageMakieExt.jl
module MyPackageMakieExt

using Makie
using MyPackage
using MyPackage: InternalType, internal_function

# Extend functions from main package
function MyPackage.plot_data(data::MyPackage.MyType)
    # Implementation using Makie
end

end # module

Loading Extensions Programmatically

ext = Base.get_extension(MyPackage, :MyPackageHeckeExt)
if ext !== nothing
    # Extension is loaded
end

Checklist

• • Add weak dependencies to [weakdeps] section
• • Add extension mapping to [extensions] section
• • Add compat entries for weak dependencies
• • Create extension module in ext/ directory
• • Use correct naming: {Package}{Trigger}Ext
• • Import and extend functions from main package
• • Load extensions in docs/make.jl for documentation
• • Add tagged tests for extension functionality

Reference

• •Patterns - Extension patterns for plotting, GPU, multiple triggers
• •WeakDepHelpers - User-friendly error messages for extensions
• •Testing & Docs - Testing extensions and documentation setup

Related Skills

• •julia-docs - Documentation setup including extensions
• •julia-tests-run - Running tests with TestItemRunner
• •julia-tests-write - Writing tests with tags
• •julia-makie-recipes - Makie plot recipes