SMatrix constructors do not all produce concrete types

[just-walk]

The constructor docstring for SMatrix indicates that not all parameters are needed if they are inferrable from the input. In particular, L is inferrable from S1 and S2.

help?> SMatrix
search: SMatrix @SMatrix DenseMatrix SizedMatrix StaticMatrix AbstractMatrix StridedMatrix

  SMatrix{S1, S2, T, L}(x::NTuple{L, T})
  SMatrix{S1, S2, T, L}(x1, x2, x3, ...)

  Construct a statically-sized matrix SMatrix. Since this type is immutable, the data must be provided upon construction
  and cannot be mutated later. The L parameter is the length of the array and is always equal to S1 * S2. Constructors
  may drop the L, T and even S2 parameters if they are inferrable from the input (e.g. L is always inferrable from S1 and
  S2).

However, dropping the L parameter produces an abstract type.

julia> typeof(SMatrix{3, 3, Float64})
UnionAll

julia> typeof(SMatrix{3, 3, Float64, 9})
DataType

julia> isconcretetype(SMatrix{3, 3, Float64})
false

julia> isconcretetype(SMatrix{3, 3, Float64, 9})
true

Is this a desired behavior? I've run into type-stability issues because of it.

[hyrodium]

Is this a desired behavior?

Not desired, but expected.

There is a LengthFreeStaticMatrices.jl package for this issue.

[jishnub]

The idea is that such a type isn't concrete by itself, but instances constructed using it would have a concrete type.