diff --git a/Project.toml b/Project.toml
index 0375150..cf3032f 100644
--- a/Project.toml
+++ b/Project.toml
@@ -6,7 +6,7 @@ version = "0.1.0"
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
 BandedMatrices = "aae01518-5342-5314-be14-df237901396f"
-DifferentialEquations = "0c46a032-eb83-5123-abaf-570d42b7fbaa"
+ComponentArrays = "b0b7db55-cfe3-40fc-9ded-d10e2dbeff66"
 FillArrays = "1a297f60-69ca-5386-bcde-b61e274b549b"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
diff --git a/examples/componentarrays.jl b/examples/componentarrays.jl
new file mode 100644
index 0000000..d142e61
--- /dev/null
+++ b/examples/componentarrays.jl
@@ -0,0 +1,39 @@
+using ComponentArrays, DualArrays
+
+
+function denselayer(layer, x)
+    layer.weight * x + layer.bias
+end
+
+
+
+# We want to different with respect to b the following function:
+
+function foo(b)
+    denselayer(ComponentVector(weight = [1 2; 3 4], bias = b), [5,6])
+end
+
+# This works as-is:
+
+foo([5,6])
+foo(DualVector([5,6], I(2)))
+
+b = DualVector([5,6], I(2))
+w = DualArray([1 2; 3 4], FourTensorIdentity((2,2), (2,2)))
+ComponentVector(weight = w, bias = b)
+
+
+denselayer(ComponentVector(weight = [1 2; 3 4], bias = b), [5,6])
+
+f = x -> x * derivative(y -> x + y, 1)
+
+
+g = (x,y) -> x + y
+f = x -> x * g(x, 1)
+
+
+
+function f(a, b)
+    a + b
+end
+
diff --git a/src/DualArrays.jl b/src/DualArrays.jl
index e4074d5..fceeff4 100644
--- a/src/DualArrays.jl
+++ b/src/DualArrays.jl
@@ -2,16 +2,21 @@ module DualArrays
 export DualVector
 
 import Base: +, ==, getindex, size, broadcast, axes, broadcasted, show, sum,
-             vcat, convert, *
+             vcat, convert, *, promote_rule
 using LinearAlgebra, ArrayLayouts, BandedMatrices, FillArrays
 
+import FillArrays: OneElementVector
+
 struct Dual{T, Partials <: AbstractVector{T}} <: Real
     value::T
     partials::Partials
 end
 
+
 ==(a::Dual, b::Dual) = a.value == b.value && a.partials == b.partials
 
+
+
 sparse_getindex(a...) = layout_getindex(a...)
 sparse_getindex(D::Diagonal, k::Integer, ::Colon) = OneElement(D.diag[k], k, size(D,2))
 sparse_getindex(D::Diagonal, ::Colon, j::Integer) = OneElement(D.diag[j], j, size(D,1))
@@ -24,7 +29,10 @@ reprents a vector of duals given by
 For now the entries just return the values.
 """
 
-struct DualVector{T, M <: AbstractMatrix{T}} <: AbstractVector{Dual{T}}
+partials_type(::Type{Matrix{T}}) where T = Vector{T}
+partials_type(::Type{<:Diagonal{T}}) where T = OneElementVector{T}
+
+struct DualVector{T, M <: AbstractMatrix{T}, Partials} <: AbstractVector{Dual{T, Partials}}
     value::Vector{T}
     jacobian::M
     function DualVector(value::Vector{T},jacobian::M) where {T, M <: AbstractMatrix{T}}
@@ -34,7 +42,7 @@ struct DualVector{T, M <: AbstractMatrix{T}} <: AbstractVector{Dual{T}}
             vector length: $x \n
             no. of jacobian rows: $y"))
         end
-        new{T,M}(value,jacobian)
+        new{T,M,partials_type(M)}(value,jacobian)
     end
 end
 
@@ -44,6 +52,18 @@ function DualVector(value::AbstractVector, jacobian::AbstractMatrix)
 end
 
 
+####
+# convert/promotion
+####
+
+# TODO: convert_eltype for M
+promote_rule(::Type{Vector{T}}, ::Type{DualVector{V,M}}) where {T,V,M} = DualVector{promote_type(T,V),M}
+convert(::Type{DualVector{V,M}}, x::AbstractVector{T}) where {T,V,M} = DualVector(convert(AbstractVector{V}, x), convert(M, Zeros(axes(x,1), axes(x,1))))
+
+
+#####
+# getindex/setindex!
+####
 
 function getindex(x::DualVector, y::Int)
     Dual(x.value[y], sparse_getindex(x.jacobian,y,:))
diff --git a/test/runtests.jl b/test/runtests.jl
index d1cba3c..fe14d88 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,4 +1,4 @@
-using DualArrays, Test, LinearAlgebra, ForwardDiff, BandedMatrices
+using DualArrays, Test, LinearAlgebra, ForwardDiff, BandedMatrices, ComponentArrays
 using DualArrays: Dual
 
 @testset "DualArrays" begin
@@ -39,4 +39,10 @@ using DualArrays: Dual
     @test vcat(x) == x
     @test vcat(x, x) == DualVector([1, 1], [1 2 3;1 2 3])
     @test vcat(x, y) == DualVector([1, 2, 3], [1 2 3;4 5 6;7 8 9])
-end
\ No newline at end of file
+
+    @testset "promote" begin
+        x = DualVector([5,6], I(2))
+        y = [7,8]
+        @test [x,y] isa Vector{<:DualVector}
+    end
+end