Modules

Syntax#

module Module; …; end
using Module
import Module

Wrap Code in a Module

The module keyword can be used to begin a module, which allows code to be organized and namespaced. Modules can define an external interface, typically consisting of exported symbols. To support this external interface, modules can have unexported internal functions and types not intended for public use.

Some modules primarily exist to wrap a type and associated functions. Such modules, by convention, are usually named with the plural form of the type’s name. For instance, if we have a module that provides a Building type, we can call such a module Buildings.

module Buildings

immutable Building
    name::String
    stories::Int
    height::Int  # in metres
end

name(b::Building) = b.name
stories(b::Building) = b.stories
height(b::Building) = b.height

function Base.show(io::IO, b::Building)
    Base.print(stories(b), "-story ", name(b), " with height ", height(b), "m")
end

export Building, name, stories, height

end

The module can then be used with the using statement:

julia> using Buildings

julia> Building("Burj Khalifa", 163, 830)
163-story Burj Khalifa with height 830m

julia> height(ans)
830

Using Modules to Organize Packages

Typically, packages consist of one or more modules. As packages grow, it may be useful to organize the main module of the package into smaller modules. A common idiom is to define those modules as submodules of the main module:

module RootModule

module SubModule1

...

end

module SubModule2

...

end

end

Initially, neither root module nor submodules have access to each others’ exported symbols. However, relative imports are supported to address this issue:

module RootModule

module SubModule1

const x = 10
export x

end

module SubModule2

# import submodule of parent module
using ..SubModule1
const y = 2x
export y

end

# import submodule of current module
using .SubModule1
using .SubModule2
const z = x + y

end

In this example, the value of RootModule.z is 30.