# Defining custom show method on REPL for custom Array
**URL:** https://discourse.julialang.org/t/defining-custom-show-method-on-repl-for-custom-array/15519
**Category:** General Usage
**Tags:** question
**Created:** [September 26, 2018, 2:38pm UTC](https://discourse.julialang.org/t/defining-custom-show-method-on-repl-for-custom-array/15519 "2018-09-26T14:38:21Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@favba](https://discourse.julialang.org/u/favba)
#### Post date: [September 26, 2018, 2:38pm UTC](https://discourse.julialang.org/t/defining-custom-show-method-on-repl-for-custom-array/15519/1 "2018-09-26T14:38:21Z")
Iām trying to define a custom `show` method for my `TestArray` below:
```julia
struct TestA{T} <: AbstractVector{T}
a::Vector{T}
b::Vector{Complex{T}}
isita::Base.RefValue{Bool}
end
TestA() = TestA{Float64}(rand(Float64,3),rand(ComplexF64,3),Ref(true))
Base.getindex(a::TestA,I) = a.a[I]
Base.size(a::TestA) = size(a.a)
```
For **interactive** usage, I want it to, based on the value of `isita`, to show either the field `a` or `b`.
That is, this behavior:
```julia
julia> a = TestA();
julia> a.isita[] = true
true
julia> a
3-element Array{Float64,1}:
0.14678500223886437
0.08462746912533947
0.8586140490403353
julia> a.isita[] = false
false
julia> a
3-element Array{Complex{Float64},1}:
0.07338388695512643 + 0.2851322043342337im
0.1638922033011161 + 0.5194807635340914im
0.4607592481784579 + 0.16060301189885262im
```
In order for that to happen, I tried defining the following:
```julia
Base.show(io::IO,::MIME"text/plain",a::TestA) = a.isita[] ? show(io,MIME"text/plain",a.a) : show(io,MIME"text/plain",a.b)
```
But that leads to this odd error message:
```julia
julia> a
Error showing value of type TestA{Float64}:
ERROR: MethodError: no method matching display(::TestA{Float64})
Closest candidates are:
display(::Any) at multimedia.jl:284
display(::AbstractDisplay, ::AbstractString, ::Any) at multimedia.jl:178
display(::AbstractString, ::Any) at multimedia.jl:179
...
Stacktrace:
[1] display(::TestA{Float64}) at ./multimedia.jl:294
[2] #invokelatest#1 at ./essentials.jl:686 [inlined]
[3] invokelatest at ./essentials.jl:685 [inlined]
[4] print_response(::IO, ::Any, ::Any, ::Bool, ::Bool, ::Any) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:154
[5] print_response(::REPL.AbstractREPL, ::Any, ::Any, ::Bool, ::Bool) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:139
[6] (::getfield(REPL, Symbol("#do_respond#40")){Bool,getfield(REPL, Symbol("##50#59")){REPL.LineEditREPL,REPL.REPLHistoryProvider},REPL.LineEditREPL,REPL.LineEdit.Prompt})(::Any, ::Any, ::Any) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:708
[7] #invokelatest#1 at ./essentials.jl:686 [inlined]
[8] invokelatest at ./essentials.jl:685 [inlined]
[9] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/LineEdit.jl:2261
[10] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:1029
[11] run_repl(::REPL.AbstractREPL, ::Any) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:191
[12] (::getfield(Base, Symbol("##720#722")){Bool,Bool,Bool,Bool})(::Module) at ./logging.jl:311
[13] #invokelatest#1 at ./essentials.jl:686 [inlined]
[14] invokelatest at ./essentials.jl:685 [inlined]
[15] macro expansion at ./logging.jl:308 [inlined]
[16] run_main_repl(::Bool, ::Bool, ::Bool, ::Bool, ::Bool) at ./client.jl:330
[17] exec_options(::Base.JLOptions) at ./client.jl:242
[18] _start() at ./client.jl:421
```
Can someone point me the right direction to get this working?
---
### Author:  [@pfitzseb](https://discourse.julialang.org/u/pfitzseb)
#### Post date: [September 26, 2018, 2:46pm UTC](https://discourse.julialang.org/t/defining-custom-show-method-on-repl-for-custom-array/15519/2 "2018-09-26T14:46:06Z")
You forgot the parens after the mime type. It should be
```julia
Base.show(io::IO,::MIME"text/plain",a::TestA) = a.isita[] ? show(io,MIME"text/plain"(),a.a) : show(io,MIME"text/plain"(),a.b)
```
or, more succinctly,
```julia
Base.show(io::IO,m::MIME"text/plain",a::TestA) = a.isita[] ? show(io,m,a.a) : show(io,m,a.b)
```
---
### Author:  [@favba](https://discourse.julialang.org/u/favba)
#### Post date: [September 26, 2018, 2:48pm UTC](https://discourse.julialang.org/t/defining-custom-show-method-on-repl-for-custom-array/15519/3 "2018-09-26T14:48:52Z")
I was so close! š