I have the following minimal example: function foo() myvar1 = 55 function bar() println(myvar1) #<- OK s = Symbol("myvar", 1) println(@eval $s) # <-ERROR: LoadError: UndefVarError: myvar1 not defined end bar() end foo() myvar2 = 77 s = Symbol("myvar", 2) prin…

I see. Is there anyway to accomplishing what I want: I want to be able to pass a digit (“1” in the case above) to the function bar, use that digit “X” to capture the variable myvarX in foo(), and use it to compute stuff within bar()? (I realize I can just send in the variable itself, but I’m trying…

What do you mean? the variable myvar1 hasn’t been defined yet when you call the function. what you are doing is equivelent to typing mynewvar2134 into the REPL. You will get an error that it is undefined.

@ pdeffebach But I did define myvar1 on row 2, before calling bar().

@eval and eval execute in global scope. myvar1 is defined in a local scope.

It is not possible using only functions. It seems that you are trying to work with metaprogramming . You can define a macro that receives an input and returns code: macro append_myvar(x) esc(Symbol(:myvar, x)) end function foo() myvar1 = 55 function bar() println(myvar1) #<- OK …

No you can’t. Do not try to construct variable names at runtime. It is also NOT possible with macros. @lucas711642 ’s post does not do anything different from writing myvar1 directly.

Yes, the code I provided only works with the 1 hard-coded in the function. You cannot pass the argument x to the macro at run time.

OP consider using a dictionary to store values instead of making variables with names generated at run time.

IMHO, using metaprogramming to create variables systematically can be quite handy in some cases. In my work, for example, I have a composite type (say MyType) that has a bunch of fields (say field1, field2, field3…). An instance of this type is passed to a function like the following: function foo(…

Not able to capture variable (via symbol) from outer scope?

New to Julia

stevengj September 17, 2020, 7:58pm 10

Yes, this seems to fall into category 3 of my list of common mis-applications of metaprogramming. See also my 2019 JuliaCon talk on why you mostly shouldn’t use metaprogramming.

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Not able to capture variable (via symbol) from outer scope?

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