# Using modules causes isa() to return the incorrect result
**URL:** https://discourse.julialang.org/t/using-modules-causes-isa-to-return-the-incorrect-result/61028
**Category:** General Usage
**Created:** [May 12, 2021, 3:18pm UTC](https://discourse.julialang.org/t/using-modules-causes-isa-to-return-the-incorrect-result/61028 "2021-05-12T15:18:05Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@anon60034542](https://discourse.julialang.org/u/anon60034542)
#### Post date: [May 12, 2021, 3:18pm UTC](https://discourse.julialang.org/t/using-modules-causes-isa-to-return-the-incorrect-result/61028/1 "2021-05-12T15:18:05Z")
```julia
# GameObj.jl
module GameObj
export GameObject
abstract type GameObject end
end
```
```julia
# WeaponObj.jl
module WeaponObj
export Weapon
include("GameObj.jl")
using .GameObj
abstract type Weapon <: GameObject end
end
```
```julia
# ChargeGunObj.jl
module ChargeGunObj
export ChargeGun
include("WeaponObj.jl")
using .WeaponObj
struct ChargeGun <: Weapon
number_of_charges::Int32
damage::Int32
function ChargeGun()
number_of_charges = 10
damage = 5
new(number_of_charges,damage)
end
end
end
```
```julia
using .ChargeGunObj
using .WeaponObj
function main()
cg :: Weapon = ChargeGun()
println(cg.damage)
end
main()
```
The problem is when I use `Weapon` as a type annotation, it returns:
```julia
LoadError: MethodError: Cannot `convert` an object of type ChargeGun
to an object of type Weapon
```
and `isa()` returns the incorrect result:
```julia
cg = ChargeGun()
println(isa(cg,Weapon)) # returns false, despite the fact that ChargeGun is a Weapon.
```
If I were to remove the modules and write everything out in the `main.jl,` it works.
---
### Author:  [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)
#### Post date: [May 12, 2021, 3:28pm UTC](https://discourse.julialang.org/t/using-modules-causes-isa-to-return-the-incorrect-result/61028/2 "2021-05-12T15:28:13Z")
The problem is that you accidentally define two different modules named `WeaponObj`. One is `Main.WeaponObj`, and one is `Main.ChargeGunObj.WeaponObj`. Your codes give something like this tree:
```nohighlight
Main
├── ChargeGunObj
│ ├── ChargeGun <: Main.ChargeGunObj.WeaponObj.Weapon
│ └── WeaponObj
│ └── Weapon
└── WeaponObj
└── Weapon
```
where, in your `main` function create a `Main.ChargeGunObj.ChargeGun` (which is a subtype of `Main.ChargeGunObj.WeaponObj.Weapon` but check if it is a subtype of `Main.WeaponObj.Weapon`. (which, while they have the same name, are not the same type, i.e. `Main.ChargeGunObj.WeaponObj.Weapon` !== `Main.WeaponObj.Weapon`).
The rule is to only `include` the same file once.
---
### Author:  [@anon60034542](https://discourse.julialang.org/u/anon60034542)
#### Post date: [May 12, 2021, 3:43pm UTC](https://discourse.julialang.org/t/using-modules-causes-isa-to-return-the-incorrect-result/61028/3 "2021-05-12T15:43:25Z")
I’m a little confused about how to fix it, do I remove the `using .WeaponObj` and just leave `using .ChargeGun`?
If I do that, `isa()` still returns `false`, and I can’t do `cg :: Weapon = ChargeGun()` because `WeaponObj` isn’t available.
---
### Author:  [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)
#### Post date: [May 12, 2021, 4:04pm UTC](https://discourse.julialang.org/t/using-modules-causes-isa-to-return-the-incorrect-result/61028/4 "2021-05-12T16:04:16Z")
How about something like this:
```nohighlight
$ cat GameObj.jl
module GameObj
export GameObject
abstract type GameObject end
end # module
$ cat WeaponObj.jl
module WeaponObj
export Weapon
# Use .. to look for GameObj in the parent module
# instead of including the file
using ..GameObj
abstract type Weapon <: GameObject end
end
$ cat ChargeGunObj.jl
module ChargeGunObj
export ChargeGun
using ..WeaponObj
struct ChargeGun <: Weapon
number_of_charges::Int32
damage::Int32
function ChargeGun()
number_of_charges = 10
damage = 5
new(number_of_charges, damage)
end
end
end
$ cat Game.jl
include("GameObj.jl")
include("WeaponObj.jl")
include("ChargeGunObj.jl")
using .GameObj, .WeaponObj, .ChargeGunObj
function main()
cg :: Weapon = ChargeGun()
println(cg.damage)
end
main()
$ julia Game.jl
5
```