# Benchmarking function in local scope
**URL:** https://discourse.julialang.org/t/benchmarking-function-in-local-scope/110228
**Category:** General Usage
**Tags:** package, benchmark, benchmarktools
**Created:** [February 14, 2024, 11:35pm UTC](https://discourse.julialang.org/t/benchmarking-function-in-local-scope/110228 "2024-02-14T23:35:46Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@leespen1](https://discourse.julialang.org/u/leespen1)
#### Post date: [February 14, 2024, 11:35pm UTC](https://discourse.julialang.org/t/benchmarking-function-in-local-scope/110228/1 "2024-02-14T23:35:46Z")
I have a function that I would like to benchmark. To that end, I would like to time the function for several different argument values, and plot how the runtime changes with the argument values. I can do this using the `@elapsed` macro, but to get a more accurate/reliable result I would like to use the `@belapsed` macro from `BenchmarkTools`. E.g.
```julia
julia> using BenchmarkTools
julia> function f()
a = "Hello World"
t = @belapsed println(a)
end
f (generic function with 1 method)
julia> f()
ERROR: UndefVarError: `a` not defined
```
I cannot use `@belapsed` because the function I am benchmarking uses variables in the local scope of the function it is called within. According to the `BenchmarkTools` documentation: " `@benchmark` is evaluated in global scope, even if called from local scope." I guess the same is true of `@belapsed`.
This is a surprising design choice to me, but I don’t see a workaround besides executing the body of the outer function in the global scope, which would be very inconvenient.
Does anyone know a workaround or another package to use so I can get a reliable estimate of the runtime for a function, even when called inside the scope of another function?
---
### Author:  [@jar1](https://discourse.julialang.org/u/jar1)
#### Post date: [February 14, 2024, 11:43pm UTC](https://discourse.julialang.org/t/benchmarking-function-in-local-scope/110228/2 "2024-02-14T23:43:35Z")
Try escaping using `println($a)`.
---
### Author:  [@leespen1](https://discourse.julialang.org/u/leespen1)
#### Post date: [February 16, 2024, 7:11pm UTC](https://discourse.julialang.org/t/benchmarking-function-in-local-scope/110228/3 "2024-02-16T19:11:39Z")
That works, thanks a bunch! I did not know that the `$` operator could be used like that. May I ask, what exactly does `$` do outside of a string? From the REPL, if I just do `$a` for some variable `a`, I get an error:
```julia
julia> $a
ERROR: syntax: "$" expression outside quote around REPL[103]:1
```
And the help string for `$` doesn’t help me much:
```julia
help?> $
search: $
$
Interpolation operator for interpolating into e.g. strings and expressions.
Examples
≡≡≡≡≡≡≡≡
julia> name = "Joe"
"Joe"
julia> "My name is $name."
"My name is Joe."
```
---
### Author:  [@jar1](https://discourse.julialang.org/u/jar1)
#### Post date: [February 16, 2024, 7:29pm UTC](https://discourse.julialang.org/t/benchmarking-function-in-local-scope/110228/4 "2024-02-16T19:29:55Z")
`$` is a feature of the BenchmarkTools.jl macros. See the docs for more details.
> If the expression you want to benchmark depends on external variables, you should use [`$` to “interpolate”](https://juliaci.github.io/BenchmarkTools.jl/stable/manual/#Interpolating-values-into-benchmark-expressions) them into the benchmark expression to [avoid the problems of benchmarking with globals](https://docs.julialang.org/en/v1/manual/performance-tips/#Avoid-global-variables). Essentially, any interpolated variable `$x` or expression `$(...)` is “pre-computed” before benchmarking begins
[https://juliaci.github.io/BenchmarkTools.jl/stable/](https://juliaci.github.io/BenchmarkTools.jl/stable/)
---
### Author:  [@leespen1](https://discourse.julialang.org/u/leespen1)
#### Post date: [February 16, 2024, 7:48pm UTC](https://discourse.julialang.org/t/benchmarking-function-in-local-scope/110228/5 "2024-02-16T19:48:56Z")
Awesome, thanks!