CODEWITHSUNDEEP
arraysjulia
Chris Rackauckas
Chris Rackauckas

Reputation: 19162

Creating an array with "hidden" extra indices

type ExtendedJumpArray{T,T2} <: AbstractArray{Float64,1}
  u::T
  jump_u::T2
end

Base.length(A::ExtendedJumpArray) = length(A.u)
Base.size(A::ExtendedJumpArray) = (length(A),)
function Base.getindex(A::ExtendedJumpArray,i::Int)
  i <= length(A.u) ? A.u[i] : A.jump_u[i-length(A.u)]
end
function Base.setindex!(A::ExtendedJumpArray,v,i::Int)
  i <= length(A.u) ? (A.u[i] = v) : (A.jump_u[i-length(A.u)] = v)
end
similar(A::ExtendedJumpArray) = deepcopy(A)
indices(A::ExtendedJumpArray) = Base.OneTo(length(A.u) + length(A.jump_u))

I thought I was the cool kid on the block, creating an array which could index past its length (I am doing it for a specific reason). But Julia apparently doesn't like this:

julia> ExtendedJumpArray([0.2],[-2.0])
Error showing value of type ExtendedJumpArray{Array{Float64,1},Array{Float64,1}}:
ERROR: MethodError: no method matching inds2string(::Int64)
Closest candidates are:
  inds2string(::Tuple{Vararg{AbstractUnitRange,N}}) at show.jl:1485
 in _summary(::ExtendedJumpArray{Array{Float64,1},Array{Float64,1}}, ::Int64) at .\show.jl:1490
 in #showarray#330(::Bool, ::Function, ::IOContext{Base.Terminals.TTYTerminal}, ::ExtendedJumpArray{Array{Float64,1},Array{Float64,1}}, ::Bool) at .\show.jl:1599
 in display(::Base.REPL.REPLDisplay{Base.REPL.LineEditREPL}, ::MIME{Symbol("text/plain")}, ::ExtendedJumpArray{Array{Float64,1},Array{Float64,1}}) at .\REPL.jl:132
 in display(::Base.REPL.REPLDisplay{Base.REPL.LineEditREPL}, ::ExtendedJumpArray{Array{Float64,1},Array{Float64,1}}) at .\REPL.jl:135
 in display(::ExtendedJumpArray{Array{Float64,1},Array{Float64,1}}) at .\multimedia.jl:143
 in print_response(::Base.Terminals.TTYTerminal, ::Any, ::Void, ::Bool, ::Bool, ::Void) at .\REPL.jl:154
 in print_response(::Base.REPL.LineEditREPL, ::Any, ::Void, ::Bool, ::Bool) at .\REPL.jl:139
 in (::Base.REPL.##22#23{Bool,Base.REPL.##33#42{Base.REPL.LineEditREPL,Base.REPL.REPLHistoryProvider},Base.REPL.LineEditREPL,Base.LineEdit.Prompt})(::Base.LineEdit.MIState, ::Base.AbstractIOBuffer{Array{UInt8,1}}, ::Bool) at .\REPL.jl:652
 in run_interface(::Base.Terminals.TTYTerminal, ::Base.LineEdit.ModalInterface) at .\LineEdit.jl:1579
 in run_frontend(::Base.REPL.LineEditREPL, ::Base.REPL.REPLBackendRef) at .\REPL.jl:903
 in run_repl(::Base.REPL.LineEditREPL, ::Base.##932#933) at .\REPL.jl:188
 in _start() at .\client.jl:360

Is there an easy way to do this without breaking the show methods, and whatever else may be broken? Or is there a better way to do this in general?

Upvotes: 2

Views: 88

Answers (1)

mbauman
mbauman

Reputation: 31362

Indices needs to return a tuple, just like size.

julia> Base.similar(A::ExtendedJumpArray) = deepcopy(A)

julia> Base.indices(A::ExtendedJumpArray) = (Base.OneTo(length(A.u) + length(A.jump_u)),)

julia> ExtendedJumpArray([0.2],[-2.0])
2-element ExtendedJumpArray{Array{Float64,1},Array{Float64,1}}:
  0.2
 -2.0

julia> length(ans)
1

Having indices and size disagree in the dimensionality of an array, though, is likely to end with confusion and strife. Some functions use size, whereas others use indices. See display vs. length above.

Upvotes: 2

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