Julia: using Vs import

using

‘using’ statement load modules, packages and exported variables, make available them for use.

operations.jl

module Arithmetic
 export addition, subtraction
 function addition(x, y)
  x+y
 end

 function subtraction(x, y)
  x-y
 end

 function mul(x, y)
  x*y
 end

 function div(x, y)
  x/y
 end
end 

sample.jl

include("operations.jl")

using Arithmetic

res1 = addition(10, 20)
res2 = subtraction(10, 20)

println("Sum of 10, 20 is $res1")
println("Subtraction of 10, 20 is $res2")

$ julia sample.jl 
Sum of 10, 20 is 30
Subtraction of 10, 20 is -10

import

‘import’ is just like using, only difference is it will not make any exported names available for use.

sample.jl

include("operations.jl")

import Arithmetic

res1 = addition(10, 20)
res2 = subtraction(10, 20)

println("Sum of 10, 20 is $res1")
println("Subtraction of 10, 20 is $res2")

$ julia sample.jl 
ERROR: LoadError: UndefVarError: addition not defined
 in include at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
 in include_from_node1 at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
 in process_options at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
 in _start at /Applications/Julia-0.4.1.app/Contents/Resources/julia/lib/julia/sys.dylib
while loading /Users/harikrishna_gurram/study1/Julia/examples/sample.jl, in expression starting on line 5

To get rid of above error, call the functions like Arithmetic.addition(10, 20), Arithmetic.subtraction(10, 20).

sample.jl

include("operations.jl")

import Arithmetic

res1 = Arithmetic.addition(10, 20)
res2 = Arithmetic.subtraction(10, 20)

println("Sum of 10, 20 is $res1")
println("Subtraction of 10, 20 is $res2")

$ julia sample.jl 
Sum of 10, 20 is 30
Subtraction of 10, 20 is -10

Import can also be used with specific names, for example

import Arithmetic: addition, subtraction

sample.jl

include("operations.jl")

import Arithmetic: addition, subtraction

res1 = addition(10, 20)
res2 = subtraction(10, 20)

println("Sum of 10, 20 is $res1")
println("Subtraction of 10, 20 is $res2")

$ julia sample.jl 
Sum of 10, 20 is 30
Subtraction of 10, 20 is -10

Note

1. You can also use following kind of syntax

using Arithmetic: addition, subtraction

2. Imported variables are read-only

3. ‘importall moduleName’ imports all names exported by the specified module.

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