# Base.getfield() gives warntype?
**URL:** https://discourse.julialang.org/t/base-getfield-gives-warntype/31845
**Category:** New to Julia
**Created:** [December 4, 2019, 10:55am UTC](https://discourse.julialang.org/t/base-getfield-gives-warntype/31845 "2019-12-04T10:55:51Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@tomtom](https://discourse.julialang.org/u/tomtom)
#### Post date: [December 4, 2019, 10:55am UTC](https://discourse.julialang.org/t/base-getfield-gives-warntype/31845/1 "2019-12-04T10:55:52Z")
I have a quite complicated parametric type that contains a simple `Int64` field like:
```julia
struct A{T, U, V, W, X, Y}
n::Int64
... (a lot of other possibly parametric-typed fields)
end
a = A(3, .....)
```
when I try to do `@code_warntype a.n`, I got a warntype like:
```julia
Body::Any
1 ─ %1 = Base.getfield(x, f)::Any
└── return %1
```
I got this situation in `v1.1.1` many times. Going to `v1.3.0` seems better, but now it comes again. Is it a bug? Thanks.
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [December 4, 2019, 11:22am UTC](https://discourse.julialang.org/t/base-getfield-gives-warntype/31845/2 "2019-12-04T11:22:35Z")
Please include a self-contained MWE.
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>
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---
### Author:  [@yuyichao](https://discourse.julialang.org/u/yuyichao)
#### Post date: [December 4, 2019, 1:15pm UTC](https://discourse.julialang.org/t/base-getfield-gives-warntype/31845/3 "2019-12-04T13:15:46Z")
No, it is just because `@code_warntype` does not do constant propagation for your input.
---
### Author:  [@rdeits](https://discourse.julialang.org/u/rdeits)
#### Post date: [December 4, 2019, 4:04pm UTC](https://discourse.julialang.org/t/base-getfield-gives-warntype/31845/4 "2019-12-04T16:04:44Z")
You’ll see that if you wrap the access in a function (which it would be as long as you’re not operating at global scope), then the `:x` is correctly constant-propagated and everything is fine:
```julia
julia> struct Foo
x::Int
y::String
end
julia> function get_x(f)
f.x
end
get_x (generic function with 1 method)
julia> f = Foo(1, "hello")
Foo(1, "hello")
julia> @code_warntype get_x(f)
Variables
#self#::Core.Compiler.Const(get_x, false)
f::Foo
Body::Int64
1 ─ %1 = Base.getproperty(f, :x)::Int64
└── return %1
```
---
### Author:  [@tomtom](https://discourse.julialang.org/u/tomtom)
#### Post date: [December 5, 2019, 3:13am UTC](https://discourse.julialang.org/t/base-getfield-gives-warntype/31845/5 "2019-12-05T03:13:58Z")
I want to include a MWE… but the case is just too complicated (needs a lot of custom types)… I could **not** reproduce the case in a simpler example…
In essence, the situation is like:
```julia
struct A
npar::Int64
end
const a = A(3)
function f(x::A)
npar = x.npar
function g()
y = 0
for i in 1:npar
y += i
end
return y
end
@code_warntype g()
end
julia> f(a)
Variables
#self#::var"#g#3"{Int64}
v::Array{Int64,1}
@_3::Union{Nothing, Tuple{Int64,Int64}}
t::Int64
Body::Array{Int64,1}
1 ─ %1 = Core.apply_type(Main.Vector, Main.Int64)::Core.Compiler.Const(Array{Int64,1}, false)
│ %2 = Core.getfield(#self#, :npar)::Int64
...
```
in **this** case, everything is fine (that’s why I said I failed to reproduce the problem in a simpler case).
However, in the **actual** situation, I got the following:
```julia
Variables
...
npar::Union{}
Body::Array{Float64,1}
1 ── Core.NewvarNode(:(threadsfor_fun))
│ Core.NewvarNode(:(grads))
...
│ %18 = Core.getfield(#self#, :npar)::Core.Box
...
8 ┄─ %24 = Core.getfield(%18, :contents)::Any
...
```
now, `Core.getfield(#self#, :npar)` has type `Core.Box` rather than `Int64`.
Another noticable difference is that `npar` is a variable (with type `Union`) in the actual case, but it’s **not** a variable in the simpler case.
any idea why it happens? thanks.
---
### Author:  [@rdeits](https://discourse.julialang.org/u/rdeits)
#### Post date: [December 5, 2019, 3:26am UTC](https://discourse.julialang.org/t/base-getfield-gives-warntype/31845/6 "2019-12-05T03:26:48Z")
Probably [performance of captured variables in closures · Issue #15276 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/15276)