# Overriding show?
**URL:** https://discourse.julialang.org/t/overriding-show/16315
**Category:** New to Julia
**Created:** [October 14, 2018, 6:31pm UTC](https://discourse.julialang.org/t/overriding-show/16315 "2018-10-14T18:31:00Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@iwelch](https://discourse.julialang.org/u/iwelch)
#### Post date: [October 14, 2018, 6:31pm UTC](https://discourse.julialang.org/t/overriding-show/16315/1 "2018-10-14T18:31:00Z")
how can I customize the (REPL) display of built-in types? I tried:
```julia
julia> Base.show(x::Int)= if (x<10) print(x) else print("large"); end;#if#
julia> show(12)
large
julia> 12 ## what is actually invoked here?
12
```
This is of course a terrible example. A more useful example would switch to scientific notation for my choice of small values. Unfortunately, a couple of my attempts here segfaulted Julia:
```julia
julia> using Printf;
julia> import Base.show
julia> show(io::IO, x::Float64)= if (x<0.01) print(io, @sprintf("%e", x)) else print(io,x); end
show (generic function with 296 methods)
julia> show( 0.0001 )
1.000000e-04
julia> show( 0.01 )
Segmentation fault: 11
```
---
### Author:  [@chakravala](https://discourse.julialang.org/u/chakravala)
#### Post date: [October 14, 2018, 6:56pm UTC](https://discourse.julialang.org/t/overriding-show/16315/2 "2018-10-14T18:56:30Z")
You left out the `io::IO` part of the `show` definition in your first exmaple. When I try it out like this
```nohighlight
julia> Base.show(io::IO,x::Int)= if (x<10) print(x) else print("large"); end
```
it actually crashes Julia for me with a stack over flow error… (not a handled Julia error, but a full crash of Julia).
---
### Author:  [@iwelch](https://discourse.julialang.org/u/iwelch)
#### Post date: [October 14, 2018, 7:00pm UTC](https://discourse.julialang.org/t/overriding-show/16315/3 "2018-10-14T19:00:10Z")
> [@chakravala](#):
>
> ```julia
> julia> Base.show(io::IO,x::Int)= if (x<10) print(x) else print("large"); end
>
> ```
mine, too. which is why I wanted to start it with a non-crasher.
---
### Author:  [@pfitzseb](https://discourse.julialang.org/u/pfitzseb)
#### Post date: [October 14, 2018, 7:15pm UTC](https://discourse.julialang.org/t/overriding-show/16315/4 "2018-10-14T19:15:44Z")
```julia
julia> Base.show(io::IO,x::Int)= if (x<10); print(io,"small"); else; print(io,"large"); end
mallC>
mallC21
large
mallC1
small
```
In your example `print(x)` calls your newly defined `show` method and that predictable creates a stack overflow. Overloading that particular method seems to mess up the Julia REPL a bit though…
---
### Author:  [@iwelch](https://discourse.julialang.org/u/iwelch)
#### Post date: [October 14, 2018, 8:21pm UTC](https://discourse.julialang.org/t/overriding-show/16315/5 "2018-10-14T20:21:51Z")
it would be best to know how to do it right, though…if it even can be done.
PS: IMHO, nothing should be able to segfault julia’s REPL.
---
### Author:  [@yuyichao](https://discourse.julialang.org/u/yuyichao)
#### Post date: [October 14, 2018, 8:30pm UTC](https://discourse.julialang.org/t/overriding-show/16315/6 "2018-10-14T20:30:53Z")
> [@iwelch](#):
>
> it would be best to know how to do it right, though…if it even can be done.
> [@iwelch](#):
>
> customize the (REPL) display of built-in types
You should’t do it so there isn’t a right way to do it.
> [@iwelch](#):
>
> IMHO, nothing should be able to segfault julia’s REPL.
That is not the case. [Crash on 'convert(::Type{Vector{T}, v::T) where T' · Issue #29562 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/29562)
---
### Author:  [@Elrod](https://discourse.julialang.org/u/Elrod)
#### Post date: [October 14, 2018, 8:42pm UTC](https://discourse.julialang.org/t/overriding-show/16315/7 "2018-10-14T20:42:28Z")
I clicked around on a few issue links, and there was an interesting discussion here:
[https://github.com/JuliaLang/julia/issues/20945](https://github.com/JuliaLang/julia/issues/20945)