Julia Package Development

Work with Julia packages in development mode: environment setup, dependency management, compilation, and debugging.

Environments vs Packages

Julia's Project.toml serves two distinct purposes:

•Environments: Self-contained workspaces for tracking dependencies
•Packages: Reusable libraries with src/ folders and module definitions

Key distinction:

•You activate environments
•You develop (dev) packages into environments
•Never activate a package directly

Development Mode Setup

julia

# Create/activate a development environment
using Pkg
Pkg.activate("./dev")

# Add your package in development mode
Pkg.develop(path="./MyPackage.jl")

# Now you can use it
using MyPackage

Interactive Development with Revise.jl

Revise.jl automatically tracks source file changes and reloads them.

julia

# In startup.jl (~/.julia/config/startup.jl)
try
    using Revise
catch e
    @warn "Error initializing Revise"
end

julia

using Revise
Pkg.activate("./dev")
Pkg.develop(path="./MyPackage.jl")
using MyPackage

# Make changes to src/MyPackage.jl
# Changes are automatically reloaded!

Common Pkg Commands

julia

using Pkg

Pkg.activate(".")               # Activate project
Pkg.instantiate()               # Install deps
Pkg.add("PackageName")          # Add package
Pkg.rm("PackageName")           # Remove package
Pkg.develop(path="...")         # Dev mode
Pkg.free("PackageName")         # Exit dev mode
Pkg.update()                    # Update all
Pkg.test()                      # Run tests
Pkg.status()                    # Show status
Pkg.precompile()                # Precompile

Logging vs Printing

Prefer logging macros over println:

julia

@debug "Debug message"
@info "Informational message"
@warn "Warning message" x
@error "Error message"

Enable debug messages:

bash

JULIA_DEBUG=MyPackage julia --project=.

Quick Reference

Task	Command
Activate project	`Pkg.activate(".")`
Install deps	`Pkg.instantiate()`
Dev mode	`Pkg.develop(path="...")`
Exit dev mode	`Pkg.free("Name")`

Reference

•Pkg Commands - Complete Pkg command reference
•Debugging - Infiltrator.jl, Debugger.jl, code exploration

Related Skills

•julia-tests-run - Running tests
•julia-tests-write - Writing tests
•julia-multipackage - Multi-package workflows