# Is this a valid way of evaluating string of code in local scope?

**URL:** <https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996>\
**Category:** Performance\
**Created:** [February 10, 2021, 2:16pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996 "2021-02-10T14:16:30Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![calebwin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/calebwin/32/14432_2.png) [@calebwin](https://discourse.julialang.org/u/calebwin)\
**Post date:** [February 10, 2021, 2:16pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996/1 "2021-02-10T14:16:31Z")

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From what I’ve read and observed, it seems like there isn’t a way of eval-ing code in local scope or otherwise without incurring significant performance penalty (lots of extra memory allocations and significantly longer run time). However, this seems like a solution for our particular use-case.

```julia
# Top-level scope here
for _ in 1:1
    data = Dict()
    while receive_request_from_aws_sqs())
        code = get_code_from_sqs()
        include_string(Main, code) # code defines a function exec_code
        function exec()
            for iter in 1:4
                @time begin
                    exec_code(data)
                end
            end
        end
        exec()
    end
end

```

Is this reasonable? Is there some part of this that looks unnecessary?

We’re using `@time` because `@btime` executes in global state so we can’t evaluate how much time it takes to operate multiple instances of code coming in from SQS. So, we’re using `@time` in a function based on our recommendation of [Performance Tips · The Julia Language](https://docs.julialang.org/en/v1/manual/performance-tips/#man-performance-abstract-container). Is that the best way of doing this.

Any input would be greatly appreciated.

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**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [February 10, 2021, 2:23pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996/2 "2021-02-10T14:23:37Z")

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No, that is not feasible. But you can write a function that returns a function. Which is probably what you want to do.

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**Author:** ![calebwin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/calebwin/32/14432_2.png) [@calebwin](https://discourse.julialang.org/u/calebwin)\
**Post date:** [February 10, 2021, 2:25pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996/3 "2021-02-10T14:25:26Z")

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Hi @pdeffebach,

Thanks for your reply but we really do need to evaluate arbitrary code that can share state stored in a dictionary. We have a serverless function that generates cache-optimized Julia code.

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<div class="post-metadata">

**Author:** ![calebwin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/calebwin/32/14432_2.png) [@calebwin](https://discourse.julialang.org/u/calebwin)\
**Post date:** [February 10, 2021, 2:37pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996/4 "2021-02-10T14:37:18Z")

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Also, if I may ask, why exactly is this infeasible? Where would I run in to issues performance or otherwise? Isn’t everything here in local scope since the whole thing is wrapped in a `for` (should it be `let`?) and `include_string` is generating a function with locally scoped variables and this function is then being called from `exec`? Where would we run into issues with this?

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<div class="post-metadata">

**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [February 10, 2021, 4:57pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996/5 "2021-02-10T16:57:44Z")

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I don’t have the expertise to explain exactly why this is infeasible. But it has to do with world age issues from modifying the global state method table inside a local scope. Hopefully someone more informed than I an can explain it more clearly.

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<div class="post-metadata">

**Author:** ![calebwin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/calebwin/32/14432_2.png) [@calebwin](https://discourse.julialang.org/u/calebwin)\
**Post date:** [February 10, 2021, 5:16pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996/6 "2021-02-10T17:16:11Z")

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Well, it is working in this case. But I’m not entirely sure why.

In the code, I note that the for loop is in top-level scope. So the `include_string` is able to create a function that can then be subsequently called. But the dictionary passed in is presumably in some sort of local scope. Or perhaps I am mistaken about that and maybe the dictionary is actually a global variable. Is there any disadvantage of that?

The `Dict` will store arbitrary values anyway (it’s effectively a `Dict{Symbol, Any}` so Julia wouldn’t be able to optimize usage of it necessarily. The function `exec_code` does create local variables produced by calling functions on `Dict` entries. Could this lead to a slowdown (for now, I’m just generating code that operates on data created in local variables but in the future I may be getting that data from the `data` dictionary)?

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<div class="post-metadata">

**Author:** ![pdeffebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pdeffebach/32/10320_2.png) [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)\
**Post date:** [February 10, 2021, 5:21pm UTC](https://discourse.julialang.org/t/is-this-a-valid-way-of-evaluating-string-of-code-in-local-scope/54996/7 "2021-02-10T17:21:34Z")

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Aside from the details about `scope` and how `include` works, if you can write a function which spits out valid Julia code, you can also write a function that returns a closure, right? Surely the second option must be easier.