# Var in for loop specification doubles execution time

**URL:** <https://discourse.julialang.org/t/var-in-for-loop-specification-doubles-execution-time/4063>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [June 2, 2017, 5:38pm UTC](https://discourse.julialang.org/t/var-in-for-loop-specification-doubles-execution-time/4063 "2017-06-02T17:38:32Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![dennis](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dennis/32/1090_2.png) [@dennis](https://discourse.julialang.org/u/dennis)\
**Post date:** [June 2, 2017, 5:38pm UTC](https://discourse.julialang.org/t/var-in-for-loop-specification-doubles-execution-time/4063/1 "2017-06-02T17:38:32Z")

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If I do

```julia
foo = 1_000_000
for i in 1:foo
  loop_body

```

the execution takes about twice as long as if I do

```julia
for i in 1:1_000_000
  loop_body

```

Using `foo = 1:1_000_000` results in a similar longer execution time.

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**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [June 2, 2017, 5:40pm UTC](https://discourse.julialang.org/t/var-in-for-loop-specification-doubles-execution-time/4063/2 "2017-06-02T17:40:28Z")

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Are you testing in the REPL / global scope, or in a function?

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<div class="post-metadata">

**Author:** ![dennis](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dennis/32/1090_2.png) [@dennis](https://discourse.julialang.org/u/dennis)\
**Post date:** [June 2, 2017, 6:59pm UTC](https://discourse.julialang.org/t/var-in-for-loop-specification-doubles-execution-time/4063/3 "2017-06-02T18:59:27Z")

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In a file run from the command line like this:

`time julia foo.jl`

In the file, the for loop is at the top level (no function).

But your question prompted me to put the for loop in a function. That made the difference and is not unexpected.