more careful with storagetypes

Author: lkdvos

src/tensors/abstracttensor.jl

@@ -74,7 +74,6 @@ similarstoragetype(::Type{TT}, ::Type{T}) where {TT <: AbstractTensorMap, T <: N
     similarstoragetype(storagetype(TT), T)
 
 # implement on arrays
-similarstoragetype(::Type{A}, ::Type{T}) where {T <: Number, A <: DenseVector{T}} = A
 Base.@assume_effects :foldable similarstoragetype(::Type{A}, ::Type{T}) where {A <: AbstractArray, T <: Number} =
     Core.Compiler.return_type(similar, Tuple{A, Type{T}, Int})
 

src/tensors/tensoroperations.jl

@@ -155,12 +155,16 @@ function TO.tensorcontract_type(
     ) where {N₁, N₂}
     spacetype(A) == spacetype(B) || throw(SpaceMismatch("incompatible space types"))
     I = sectortype(A)
-    M = similarstoragetype(A, sectorscalartype(I) <: Real ? TC : complex(TC))
-    MB = similarstoragetype(B, sectorscalartype(I) <: Real ? TC : complex(TC))
-    M == MB || throw(ArgumentError("incompatible storage types:\n$(M) ≠ $(MB)"))
+    TC′ = isreal(I) ? TC : complex(TC)
+    M = pomote_storagetype(similarstoragetype(A, TC′), similarstoragetype(B, TC′))
     return tensormaptype(spacetype(A), N₁, N₂, M)
 end
 
+# TODO: handle actual promotion rule system
+function promote_storagetype(::Type{M₁}, ::Type{M₂}) where {M₁, M₂}
+    return M₁ === M₂ ? M₁ : throw(ArgumentError("Cannot determine storage type for combining `$M₁` and `$M₂`"))
+end
+
 function TO.tensorcontract_structure(
         A::AbstractTensorMap, pA::Index2Tuple, conjA::Bool,
         B::AbstractTensorMap, pB::Index2Tuple, conjB::Bool,