Add LinearOperatorException for non-concrete S in Diag, Normal and ProdOps

Author: nHackel

src/DiagOp.jl

@@ -43,6 +43,7 @@ function DiagOp(ops)
     ncol += size(ops[i], 2)
     S = promote_type(S, LinearOperators.storage_type(ops[i]))
   end
+  isconcretetype(S) || throw(LinearOperatorException("Storage types cannot be promoted to a concrete type"))
 
   xIdx = cumsum(vcat(1,[size(ops[i], 2) for i=1:length(ops)]))
   yIdx = cumsum(vcat(1,[size(ops[i], 1) for i=1:length(ops)]))
@@ -136,6 +137,7 @@ end
 function LinearOperatorCollection.normalOperator(diag::DiagOp, W=opEye(eltype(diag), size(diag,1), S = LinearOperators.storage_type(diag)); copyOpsFn = copy, kwargs...)
   T = promote_type(eltype(diag), eltype(W))
   S = promote_type(LinearOperators.storage_type(diag), LinearOperators.storage_type(W))
+  isconcretetype(S) || throw(LinearOperatorException("Storage types cannot be promoted to a concrete type"))
   tmp = S(undef, diag.nrow)
   tmp .= one(eltype(diag))
   weights = W*tmp

src/NormalOp.jl

@@ -39,6 +39,7 @@ LinearOperators.storage_type(op::NormalOpImpl) = typeof(op.Mv5)
 
 function NormalOpImpl(parent, weights)
   S = promote_type(storage_type(parent), storage_type(weights))
+  isconcretetype(S) || throw(LinearOperatorException("Storage types cannot be promoted to a concrete type"))
   tmp = S(undef, size(parent, 1))
   return NormalOpImpl(parent, weights, tmp)
 end

src/ProdOp.jl

@@ -36,7 +36,8 @@ composition/product of two Operators. Differs with * since it can handle normal
 function ProdOp(A, B)
   nrow = size(A, 1)
   ncol = size(B, 2)
-  S = promote_type(storage_type(A), storage_type(B))
+  S = promote_type(LinearOperators.storage_type(A), LinearOperators.storage_type(B))
+  isconcretetype(S) || throw(LinearOperatorException("Storage types cannot be promoted to a concrete type"))
   tmp_ = S(undef, size(B, 1))
 
   function produ!(res, x::AbstractVector{T}, tmp) where T<:Union{Real,Complex}