show function of ExtendableGrid throws error

[pjaap]

ExtendableGrids v1.10.4
Julia 1.11.0

In REPL, a simple

julia> using ExtendableGrids
julia> ExtendableGrid{Float64,Int32}()

throws an error trying to show the object:

Error showing value of type ExtendableGrid{Float64, Int64}:
ERROR: MethodError: no method matching instantiate(::ExtendableGrid{Float64, Int64}, ::Type{Coordinates})
The function `instantiate` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  instantiate(::ExtendableGrid{Tc, Ti}, ::Type{EdgeRegions}) where {Tc, Ti}
   @ ExtendableGrids ~/.julia/packages/ExtendableGrids/7u1Kj/src/derived.jl:1186
  instantiate(::ExtendableGrid{Tc, Ti}, ::Type{FaceNodes}) where {Tc, Ti}
   @ ExtendableGrids ~/.julia/packages/ExtendableGrids/7u1Kj/src/derived.jl:162
  instantiate(::ExtendableGrid{Tc, Ti}, ::Type{BFaceFaces}) where {Tc, Ti}
   @ ExtendableGrids ~/.julia/packages/ExtendableGrids/7u1Kj/src/derived.jl:1025
  ...

Stacktrace:
  [1] (::ExtendableGrids.var"#7#8"{ExtendableGrid{Float64, Int64}, DataType})()
    @ ExtendableGrids ~/.julia/packages/ExtendableGrids/7u1Kj/src/extendablegrid.jl:272
  [2] get!(default::ExtendableGrids.var"#7#8"{ExtendableGrid{Float64, Int64}, DataType}, h::Dict{Type{<:AbstractGridComponent}, Any}, key::Type{Coordinates})
    @ Base ./dict.jl:458
  [3] get!
    @ ~/.julia/packages/ExtendableGrids/7u1Kj/src/extendablegrid.jl:272 [inlined]
  [4] getindex(grid::ExtendableGrid{Float64, Int64}, T::Type{Coordinates})
    @ ExtendableGrids ~/.julia/packages/ExtendableGrids/7u1Kj/src/extendablegrid.jl:63
  [5] dim_space
    @ ~/.julia/packages/ExtendableGrids/7u1Kj/src/extendablegrid.jl:356 [inlined]
  [6] show(io::IOContext{Base.TTY}, grid::ExtendableGrid{Float64, Int64})
    @ ExtendableGrids ~/.julia/packages/ExtendableGrids/7u1Kj/src/extendablegrid.jl:545
  [7] show(io::IOContext{Base.TTY}, ::MIME{Symbol("text/plain")}, x::ExtendableGrid{Float64, Int64})
    @ Base.Multimedia ./multimedia.jl:47
  [8] (::REPL.var"#68#69"{REPL.REPLDisplay{REPL.LineEditREPL}, MIME{Symbol("text/plain")}, Base.RefValue{Any}})(io::Any)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:348
  [9] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:646
 [10] display(d::REPL.REPLDisplay, mime::MIME{Symbol("text/plain")}, x::Any)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:334
 [11] display
    @ /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:353 [inlined]
 [12] display(x::Any)
    @ Base.Multimedia ./multimedia.jl:340
 [13] #invokelatest#2
    @ ./essentials.jl:1054 [inlined]
 [14] invokelatest
    @ ./essentials.jl:1051 [inlined]
 [15] print_response(errio::IO, response::Any, show_value::Bool, have_color::Bool, specialdisplay::Union{Nothing, AbstractDisplay})
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:390
 [16] (::REPL.var"#70#71"{REPL.LineEditREPL, Pair{Any, Bool}, Bool, Bool})(io::Any)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:359
 [17] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:646
 [18] print_response(repl::REPL.AbstractREPL, response::Any, show_value::Bool, have_color::Bool)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:357
 [19] (::REPL.var"#do_respond#96"{Bool, Bool, REPL.var"#112#130"{REPL.LineEditREPL, REPL.REPLHistoryProvider}, REPL.LineEditREPL, REPL.LineEdit.Prompt})(s::REPL.LineEdit.MIState, buf::Any, ok::Bool)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:988
 [20] #invokelatest#2
    @ ./essentials.jl:1054 [inlined]
 [21] invokelatest
    @ ./essentials.jl:1051 [inlined]
 [22] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
    @ REPL.LineEdit /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/LineEdit.jl:2749
 [23] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:1456
 [24] (::REPL.var"#75#81"{REPL.LineEditREPL, REPL.REPLBackendRef})()
    @ REPL /usr/local/julia/share/julia/stdlib/v1.11/REPL/src/REPL.jl:461

[j-fu]

Well, yes, never tried to create this kind of empty grid in the repl.

IMHO dim_space, num_nodes, num_cells, num_bfaces should return 0 if there
are no Coordinates, CellNodes, BFaceNodes. This would fix this.

[pjaap]

I'll fix this if you want and add tests for some default constructors. I think this is an important issue since it scares beginners of Julia when they discover things in the REPL, like it did when I encountered this problem.

[pjaap]

See #71