Using `:` for indexing does not works on `TransferFunction`

[franckgaga]

Hi,

It seems that the : operator for indexing all the elements does not work on TransferFunction. These lines:

sys = append(tf(2, [10, 1]), tf(3, [5, 1]))
sys[:, 1]

results in:

ERROR: MethodError: no method matching length(::Colon)

Closest candidates are:
  length(::Union{Base.KeySet, Base.ValueIterator})
   @ Base abstractdict.jl:58
  length(::Union{SparseArrays.FixedSparseVector{Tv, Ti}, SparseArrays.SparseVector{Tv, Ti}} where {Tv, Ti})
   @ SparseArrays ~/.julia/juliaup/julia-1.9.3+0.x64.linux.gnu/share/julia/stdlib/v1.9/SparseArrays/src/sparsevector.jl:95
  length(::Union{IterTools.Properties, IterTools.PropertyValues})
   @ IterTools ~/.julia/packages/IterTools/CtkIT/src/IterTools.jl:1010
  ...

Stacktrace:
 [1] getindex(::TransferFunction{Continuous, ControlSystemsBase.SisoRational{Int64}}, ::Function, ::Int64)
   @ ControlSystemsBase ~/.julia/packages/ControlSystemsBase/X6e5r/src/types/TransferFunction.jl:58
 [2] top-level scope
   @ REPL[10]:1

Thanks !

Francis Gagnon

[franckgaga]

Thanks Fredrik!