AssertionError in show for Vector{Pair{Int64,Vector{Float64}}}

[tkoolen]

julia> [1 => rand(3)]
1-element Array{Pair{Int64,Array{Float64,1}},1}:
Error showing value of type Array{Pair{Int64,Array{Float64,1}},1}:
ERROR: AssertionError: Array{Float64,1} is not a subtype of Pair{Int64,Array{Float64,1}}
Stacktrace:
 [1] typeinfo_prefix(::IOContext{Base.GenericIOBuffer{Array{UInt8,1}}}, ::Array{Float64,1}) at ./arrayshow.jl:477
 [2] show_vector(::IOContext{Base.GenericIOBuffer{Array{UInt8,1}}}, ::Array{Float64,1}, ::Char, ::Char) at ./arrayshow.jl:431 (repeats 2 times)
 [3] show at ./arrayshow.jl:417 [inlined]
 [4] show(::IOContext{Base.GenericIOBuffer{Array{UInt8,1}}}, ::Pair{Int64,Array{Float64,1}}) at ./show.jl:585
 [5] #sprint#336(::IOContext{REPL.Terminals.TTYTerminal}, ::Int64, ::Function, ::Function, ::Pair{Int64,Array{Float64,1}}) at ./strings/io.jl:97
 [6] #sprint at ./<missing>:0 [inlined]
 [7] alignment(::IOContext{REPL.Terminals.TTYTerminal}, ::Pair{Int64,Array{Float64,1}}) at ./show.jl:1801
 [8] alignment(::IOContext{REPL.Terminals.TTYTerminal}, ::Array{Pair{Int64,Array{Float64,1}},1}, ::Base.OneTo{Int64}, ::Base.OneTo{Int64}, ::Int64, ::Int64, ::Int64) at ./arrayshow.jl:68
 [9] print_matrix(::IOContext{REPL.Terminals.TTYTerminal}, ::Array{Pair{Int64,Array{Float64,1}},1}, ::String, ::String, ::String, ::String, ::String, ::String, ::Int64, ::Int64) at ./arrayshow.jl:186
 [10] print_matrix at ./arrayshow.jl:159 [inlined]
 [11] print_array at ./arrayshow.jl:308 [inlined]
 [12] show(::IOContext{REPL.Terminals.TTYTerminal}, ::MIME{Symbol("text/plain")}, ::Array{Pair{Int64,Array{Float64,1}},1}) at ./arrayshow.jl:344
 [13] display(::REPL.REPLDisplay{REPL.LineEditREPL}, ::MIME{Symbol("text/plain")}, ::Array{Pair{Int64,Array{Float64,1}},1}) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:130
 [14] display(::REPL.REPLDisplay{REPL.LineEditREPL}, ::Array{Pair{Int64,Array{Float64,1}},1}) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:133
 [15] display(::Array{Pair{Int64,Array{Float64,1}},1}) at ./multimedia.jl:287
 [16] #invokelatest#1 at ./essentials.jl:667 [inlined]
 [17] invokelatest at ./essentials.jl:666 [inlined]
 [18] print_response(::REPL.Terminals.TTYTerminal, ::Any, ::Nothing, ::Bool, ::Bool, ::Nothing) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:151
 [19] print_response(::REPL.LineEditREPL, ::Any, ::Nothing, ::Bool, ::Bool) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:137
 [20] (::getfield(REPL, Symbol("#do_respond#42")){Bool,getfield(REPL, Symbol("##52#61")){REPL.LineEditREPL,REPL.REPLHistoryProvider},REPL.LineEditREPL,REPL.LineEdit.Prompt})(::REPL.LineEdit.MIState, ::Base.GenericIOBuffer{Array{UInt8,1}}, ::Bool) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:705
 [21] top-level scope

julia> versioninfo()
Julia Version 0.7.0-DEV.5245
Commit fb0d289814 (2018-05-29 12:44 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin14.5.0)
  CPU: Intel(R) Core(TM) i7-3820QM CPU @ 2.70GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, ivybridge)

[KristofferC]

#25466, #26881, #26256, #25042, not saying this is an exact dup but something is just not good with the way things are done now

[JeffBezanson]

Would be fixed by #26602; only question is how many more of those PRs will be needed over the years...

[StefanKarpinski]

There's definitely something rotten about this approach that we need to fix. I have noted it in my collection of potentially unstable APIs document.

[JeffBezanson]

My analysis and suggested fix:
#25857 (comment)
#26881 (comment)

[JeffBezanson]

Actually this does seem to be an exact dup of #25466.