Development workflow

Project setup

Julia has an built-in function Pkg.generate which generates the minimal file structure for a new project. For example, to initialize a project called ULG all you need to do is run the following commands.

julia> using Pkg

julia> Pkg.generate("ULG.jl")
  Generating  project ULG:
    ULG.jl/Project.toml
    ULG.jl/src/ULG.jl
Dict{SubString{String}, Base.UUID} with 1 entry:
  "ULG" => UUID("7f50121b-566d-49a5-8387-754b659c937e")

This writes two important files to disk.

• Project.toml contains metainformation about the project and (optionally) a list of required packages including their version restrictions.

• src/ULG.jl the main code file where the ULG module is defined.

To load and use the ULG package first activate the package environment then load the code with using ULG.

Modules

Modules are a way of organizing code in Julia. For example, each package is a module of its own. Above we generated the ULG module. After loading it all of the function and variables can not be used directly since they are in the module's own namespace. Thus, we have to prepend ULG. e.g. ULG.greet(). It is also inconvenient to put all of your code into a single file. Julia provides the include function which behaves as if the contents of the source file were written in the ULG.jl file.

As we have already seen in the exercise of the Functions#Syntax section with mean we do not always have to put the module name in front of the function. Julia achieves this with the export keyword. In order to make the ULG.greet function available inside of the global scope (after using ULG) we just add the line export greet to src/ULG.jl.

Testing

When we are done programming our package it is always good practice to write unit tests. These code snippets test whether our code behaves as intended. Start by creating the test/ folder and put a file called runtests.jl inside it. This file tells Julia how to run all tests. In order to test ULG.greet we could for example add these lines.

using Test
using ULG

@testset begin
    @test isnothing(ULG.greet())
    @test 1 + 1 == 3
end

Then we can run these tests with

(ULG) pkg> add Test

(ULG) pkg> test

Test Summary: | Pass  Fail  Total  Time
test set      |    1     1      2  0.5s
ERROR: LoadError: Some tests did not pass: 1 passed, 1 failed, 0 errored, 0 broken.
in expression starting at /tmp/ULG/test/runtests.jl:4
ERROR: Package ULG errored during testing

Revise

After we have changed existing code Julia needs to recompile it. Depending on the package size restarting Julia for this can take a while. However, we do not necessarily have to exit Julia since only the files containing the changes need to be reloaded. Revise automates this task.

julia> using Revise

julia> using ULG

# here we edit some code

julia> revise()

# new code is loaded without restarting