# Appropriate warning for size using code\_warntype
**URL:** https://discourse.julialang.org/t/appropriate-warning-for-size-using-code-warntype/105457
**Category:** Performance
**Created:** [October 27, 2023, 1:19am UTC](https://discourse.julialang.org/t/appropriate-warning-for-size-using-code-warntype/105457 "2023-10-27T01:19:46Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Jake](https://discourse.julialang.org/u/Jake)
#### Post date: [October 27, 2023, 1:19am UTC](https://discourse.julialang.org/t/appropriate-warning-for-size-using-code-warntype/105457/1 "2023-10-27T01:19:46Z")
I tried profiling some code using JET. When I used size() on a matrix of type Any, the warning came back that the output of the function _size_ is of type Any. This confused me because I thought size could only output of type Int. I created a MWE and duplicated the effect with @code\_warntype as shown below
```julia
julia> function mwe()
a = [1 2.0; true "Yes"]
b = size(a, 1)
end
mwe (generic function with 1 method)
julia> typeof(mwe())
Int64
julia> @code_warntype mwe()
MethodInstance for mwe()
from mwe() @ Main REPL[10]:1
Arguments
#self#::Core.Const(mwe)
Locals
b::Any
a::Any
Body::Any
1 ─ %1 = Core.tuple(2, 2)::Core.Const((2, 2))
│ (a = Base.hvcat(%1, 1, 2.0, true, "Yes"))
│ %3 = Main.size(a, 1)::Any
│ (b = %3)
└── return %3
```
If I read this right, size returns an Int64, but @code\_warntype shows that it returns a type of Any. JET shows the same thing.
Does this mean the compiler does not know what the type of size(a::Any,1) is and I should make the statement Int(size(a,1)) in my code or is this a bug in @code\_warntype?
---
### Author:  [@aviatesk](https://discourse.julialang.org/u/aviatesk)
#### Post date: [October 27, 2023, 4:38am UTC](https://discourse.julialang.org/t/appropriate-warning-for-size-using-code-warntype/105457/2 "2023-10-27T04:38:44Z")
Firstly, it’s worth noting that what’s considered as problematic can differ based on the situation. However, in terms of performance of this function itself, the real issue isn’t the return type of `size(a, 1)` being non-inferred, but it is that the type of `a` isn’t inferred as `Matrix{Any}`. This causes a runtime dispatch to `size(a, 1)`, eventually leading to inaccurate return type of this function itself as a whole. I’m guessing you’ve used JET’s `@report_opt`, which should’ve reported this runtime dispatch. In contrast, `@report_call` doesn’t highlight such concern by default, since it’s designed to be permissive as runtime dispatches in general doesn’t necessarily mean `MethodError` (so JET doesn’t consider it as very problematic in terms of error detection point of view). Anyway, circling back, a quick fix here could be to use a type annotation like `a = [1 2.0; true "Yes"]::Matrix{Any}`:
```julia
julia> function mwe()
a = [1 2.0; true "Yes"]::Matrix{Any} # help the compiler
b = size(a, 1)
end
mwe (generic function with 1 method)
julia> @code_warntype mwe()
MethodInstance for mwe()
from mwe() @ Main REPL[6]:1
Arguments
#self#::Core.Const(mwe)
Locals
b::Int64
a::Matrix{Any}
Body::Int64
1 ─ %1 = Core.tuple(2, 2)::Core.Const((2, 2))
│ %2 = Base.hvcat(%1, 1, 2.0, true, "Yes")::Any
│ %3 = Core.apply_type(Main.Matrix, Main.Any)::Core.Const(Matrix{Any})
│ (a = Core.typeassert(%2, %3))
│ %5 = Main.size(a, 1)::Int64
│ (b = %5)
└── return %5
```
Although tweaking the implementation of `Base.typed_hvcat` is an alternative and probably better option, it’d involve changes to Julia Base itself.
---
### Author:  [@jishnub](https://discourse.julialang.org/u/jishnub)
#### Post date: [October 27, 2023, 8:39am UTC](https://discourse.julialang.org/t/appropriate-warning-for-size-using-code-warntype/105457/3 "2023-10-27T08:39:12Z")
> [@Jake](#):
>
> because I thought size could only output of type Int
This isn’t strictly necessary, as `BigInt` ranges have a `BigInt` size, and infinite arrays have an infinite size.