Various errors with zero-size vectors and matrices

[rdeits]

Fixed-size vectors and matrices with one or more dimensions of zero length can cause various different issues when constructed:

julia> using FixedSizeArrays

julia> m = Mat{0, 0, Float64}()
FixedSizeArrays.Mat{0,0,Float64}(
)


julia> m = Mat{0, 0, Float64}(0)
ERROR: type Union has no field name
 in fsa_abstract at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:46
 in size_or at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:52
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/constructors.jl:77
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/FixedSizeArrays.jl:18

julia> m = Mat{0, 1, Float64}()
ERROR: MethodError: `convert` has no method matching convert(::Type{Tuple{Tuple{}}}, ::Tuple{})
This may have arisen from a call to the constructor Tuple{Tuple{}}(...),
since type constructors fall back to convert methods.
Closest candidates are:
  call{T}(::Type{T}, ::Any)
  convert{T<:Tuple{Any,Vararg{Any}}}(::Type{T<:Tuple{Any,Vararg{Any}}}, ::T<:Tuple{Any,Vararg{Any}})
  convert{T<:Tuple{Any,Vararg{Any}}}(::Type{T<:Tuple{Any,Vararg{Any}}}, ::Tuple{Any,Vararg{Any}})
  ...
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/constructors.jl:92

julia> m = Mat{0, 1, Float64}(0)
ERROR: type Union has no field name
 in fsa_abstract at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:46
 in size_or at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:52
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/constructors.jl:77
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/FixedSizeArrays.jl:18

julia> m = Mat{1, 0, Float64}()
FixedSizeArrays.Mat{1,0,Float64}(
Error showing value of type FixedSizeArrays.Mat{1,0,Float64}:
ERROR: TypeError: show: in new, expected FixedSizeArrays.Mat{1,0,Float64}, got FixedSizeArrays.Mat{0,1,Union{}}
 in show at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/FixedSizeArrays.jl:44
 in anonymous at show.jl:1299
 in with_output_limit at ./show.jl:1276
 in showlimited at show.jl:1298
 in writemime at replutil.jl:4
 in display at REPL.jl:114
 in display at REPL.jl:117
 [inlined code] from multimedia.jl:151
 in display at multimedia.jl:163
 in print_response at REPL.jl:134
 in print_response at REPL.jl:121
 in anonymous at REPL.jl:624
 in anonymous at REPL.jl:827
 in anonymous at LineEdit.jl:767
 in prompt! at ./LineEdit.jl:1636
 in run_interface at ./LineEdit.jl:1605
 in run_frontend at ./REPL.jl:863
 in run_repl at ./REPL.jl:167
 in _start at ./client.jl:420

julia> m = Mat{1, 0, Float64}(0)
ERROR: type Union has no field name
 in fsa_abstract at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:46
 in size_or at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:52
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/constructors.jl:77
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/FixedSizeArrays.jl:18

julia> m = Vec{0, Float64}()
FixedSizeArrays.Vec{0,Float64}(())

julia> m = Vec{0, Float64}(0)
ERROR: type Union has no field name
 in fsa_abstract at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:46
 in size_or at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:52
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/constructors.jl:77
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/FixedSizeArrays.jl:26

I'll see if I can tell what's going on.

[rdeits]

Actually, the 1x0 Mat constructor with no args works now with FixedSizeArrays master.

[rdeits]

I don't understand quite what's going on here. The simplest failing case is:

julia> using FixedSizeArrays

julia> Vec{0, Int}(0)
ERROR: type Union has no field name
 in fsa_abstract at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:46
 in size_or at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/core.jl:52
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/constructors.jl:78
 in call at /home/rdeits/.julia/v0.4/FixedSizeArrays/src/FixedSizeArrays.jl:26

It fails because the typevar FSA in call() is Union{}, not any actual FSA type.

[SimonDanisch]

May I ask why you would like to do this? I agree, the error messages should be clearer, but is there a case to make this possible at all?
Vec{0, Int}(0) should clearly throw an ArgumentError, no?

[rdeits]

I'm not actually sure. I came across this bug while working on some code for representing linear systems (i.e. systems of the form xdot = A*x), and I occasionally end up with systems in which the length of x is 0. Being able to initialize 0-element vectors the same way I initialize vectors of any other length just lets me remove some special cases from my code.

I think it's also somewhat analogous to the built-in zeros(0), which returns a 0-element Array. In my mind, asking for a zero-element vector full of zeros is a well-formed (if slightly odd) thing to do.

That said, it's also easy for me to work around this by adding a few extra definitions to my code, e.g.:

call{T}(::Type{Mat{0, 0, T}}, x::Number) = Mat{0,0,T}()
call{N, T}(::Type{Mat{0, N, T}}) = Mat{0, N, T}(tuple([tuple() for i in 1:N]...))
call{N, T}(::Type{Mat{0, N, T}}, x::Number) = Mat{0, N, T}()
call{M, T}(::Type{Mat{M, 0, T}}, x::Number) = Mat{M, 0, T}()

and so on.

[SimonDanisch]

If you're convinced that this is the correct behaviour, I wouldn't mind a PR ;)
I'm not that convinced, that Mat{0,0,T}(0) is correct behaviour, though :D
There is zero for that:

zero(Mat{0,0, Float32})
zero(Mat{0,10, Float32})

I guess this discussion is slightly similar to this one: #75 (comment)

[rdeits]

Ah, of course! I'd forgotten about the overloaded zero(). I'll switch to using that in my code, which should solve my problem nicely. Thanks!

For what it's worth, I started out using Vec{N,T}(0) instead of zero(Vec{N, T}) because I saw the former in the readme and assumed that was the best way to construct a vector of zeros. But using zero() does make a Julian kind of sense.

[tkoolen]

I'm encountering a related issue with the transpose of an Nx0 Mat:

julia> a = Mat{3, 0, Float64}()
FixedSizeArrays.Mat{3,0,Float64}(



)

julia> a'
FixedSizeArrays.Mat{3,1,Tuple{}}(
    ()
    ()
    ()
)

[SimonDanisch]

I fixed it in #126

[tkoolen]

Great, thank you!