# Interpolating symbol in @eval expression
**URL:** https://discourse.julialang.org/t/interpolating-symbol-in-eval-expression/27396
**Category:** General Usage
**Tags:** metaprogramming
**Created:** [August 10, 2019, 4:23pm UTC](https://discourse.julialang.org/t/interpolating-symbol-in-eval-expression/27396 "2019-08-10T16:23:18Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@tk3369](https://discourse.julialang.org/u/tk3369)
#### Post date: [August 10, 2019, 4:23pm UTC](https://discourse.julialang.org/t/interpolating-symbol-in-eval-expression/27396/1 "2019-08-10T16:23:19Z")
In this example, I’m trying to define functions for accessing data frame columns. However, the interpolation within the `getindex` call ended up with a type rather than the original symbol… Why is that? What can I do to fix it?
```julia
julia> module Foo
using DataFrames
for f in (:x, :y)
@eval $(f)(df::AbstractDataFrame) = df[:, $f]
end
end
Main.Foo
julia> df = DataFrame(x = rand(3), y = rand(3))
3×2 DataFrame
│ Row │ x │ y │
│ │ Float64 │ Float64 │
├─────┼──────────┼──────────┤
│ 1 │ 0.206567 │ 0.238623 │
│ 2 │ 0.467982 │ 0.219791 │
│ 3 │ 0.219056 │ 0.158868 │
julia> Foo.x(df)
ERROR: MethodError: no method matching getindex(::DataFrame, ::Colon, ::typeof(Main.Foo.x))
Closest candidates are:
getindex(::DataFrame, ::Colon) at /Users/tomkwong/.julia/packages/DataFrames/0Em9Q/src/dataframe/dataframe.jl:306
getindex(::DataFrame, ::Colon, ::Colon) at /Users/tomkwong/.julia/packages/DataFrames/0Em9Q/src/dataframe/dataframe.jl:381
getindex(::DataFrame, ::Colon, ::Union{Signed, Symbol, Unsigned}) at /Users/tomkwong/.julia/packages/DataFrames/0Em9Q/src/dataframe/dataframe.jl:358
```
---
### Author:  [@tk3369](https://discourse.julialang.org/u/tk3369)
#### Post date: [August 10, 2019, 4:26pm UTC](https://discourse.julialang.org/t/interpolating-symbol-in-eval-expression/27396/2 "2019-08-10T16:26:36Z")
Interestingly, `getproperty` works. I still don’t understand why the other syntax failed though…
```julia
julia> module Foo
using DataFrames
for f in (:x, :y)
@eval $(f)(df::AbstractDataFrame) = df.$(f)
end
end
Main.Foo
julia> Foo.x(df)
3-element Array{Float64,1}:
0.20656716839978007
0.4679817773900221
0.21905643202268887
```
---
### Author:  [@yuyichao](https://discourse.julialang.org/u/yuyichao)
#### Post date: [August 10, 2019, 4:34pm UTC](https://discourse.julialang.org/t/interpolating-symbol-in-eval-expression/27396/3 "2019-08-10T16:34:16Z")
No it did not end up with a type.
> [@tk3369](#):
>
> getindex(::DataFrame, ::Colon, ::typeof(Main.Foo.x))
Simply shows you the type. The value you pass in is of type `typeof(Main.Foo.x)`, i.e. you passed in `Main.Foo.x`.
This is because what you write is simply `x(df::AbstractDataFrame) = df[:, x]`, which you can see yourself by printing the result of the interpolation. You probably want `x(df::AbstractDataFrame) = df[:, :x]` instead which means that you should interpolate the quoted symbol rather than passing in the symbol directly. You can figure out what to pass in by looking at `:(:x)` and in this case one way to do it is `$(QuoteNode(f))`
---
### Author:  [@tk3369](https://discourse.julialang.org/u/tk3369)
#### Post date: [August 10, 2019, 4:39pm UTC](https://discourse.julialang.org/t/interpolating-symbol-in-eval-expression/27396/4 "2019-08-10T16:39:42Z")
Perfect, thanks!