Patterns are not hashable

[jkrumbiegel]

Because of the AbstractMatrix supertype, an overload kicks in that tries to call getindex which we don't define.

julia> Set([Pattern('/')])
ERROR: CanonicalIndexError: getindex not defined for Makie.LinePattern
Stacktrace:
  [1] error_if_canonical_getindex(::IndexCartesian, ::Makie.LinePattern, ::Int64, ::Int64)
    @ Base ./abstractarray.jl:1327
  [2] getindex
    @ ./abstractarray.jl:1311 [inlined]
  [3] _getindex
    @ ./abstractarray.jl:1358 [inlined]
  [4] getindex
    @ ./abstractarray.jl:1312 [inlined]
  [5] iterate
    @ ./abstractarray.jl:1209 [inlined]
  [6] iterate
    @ ./abstractarray.jl:1207 [inlined]
  [7] hash
    @ ./abstractarray.jl:3549 [inlined]
  [8] hash
    @ ./hashing.jl:28 [inlined]
  [9] hashindex
    @ ./dict.jl:128 [inlined]
 [10] ht_keyindex2_shorthash!(h::Dict{Makie.LinePattern, Nothing}, key::Makie.LinePattern)
    @ Base ./dict.jl:274
 [11] setindex!(h::Dict{Makie.LinePattern, Nothing}, v0::Nothing, key::Makie.LinePattern)
    @ Base ./dict.jl:356
 [12] push!
    @ ./set.jl:137 [inlined]
 [13] union!(s::Set{Makie.LinePattern}, itr::Vector{Makie.LinePattern})
    @ Base ./abstractset.jl:106
 [14] Set
    @ ./set.jl:47 [inlined]
 [15] _Set
    @ ./set.jl:59 [inlined]
 [16] Set(itr::Vector{Makie.LinePattern})
    @ Base ./set.jl:58
 [17] top-level scope
    @ REPL[15]:1

[ffreyer]

I don't think there is a strong reason to have it inherit from AbstractMatrix. I think that's just there because Patterns are more or less an image.

In what context are we using hashing again? Was is it for svg/pdf saving in CairoMakie?

[jkrumbiegel]

It came up for me in AlgebraOfGraphics where a set of attributes can be computed to check for duplicates