Require weight and bias to be AbstractArrays

src/layers/basic.jl

@@ -102,7 +102,7 @@ julia> d(rand(5))
   -0.16210233
    0.12311903```
 """
-struct Dense{F,S,T}
+struct Dense{F,S<:AbstractArray,T<:AbstractArray}
   W::S
   b::T
   σ::F

test/layers/basic.jl

@@ -28,6 +28,13 @@ import Flux: activations
   end
 
   @testset "Dense" begin
+    @testset "constructors" begin
+      @test size(Dense(10, 100).W) == (100, 10)
+      @test Dense(rand(100,10), rand(10)).σ == identity
+
+      @test_throws MethodError Dense(10, 10.5)
+    end
+
     @test  length(Dense(10, 5)(randn(10))) == 5
     @test_throws DimensionMismatch Dense(10, 5)(randn(1))
     @test_throws MethodError Dense(10, 5)(1) # avoid broadcasting
@@ -37,7 +44,6 @@ import Flux: activations
     @test Dense(10, 1, identity, initW = ones, initb = zeros)(ones(10,2)) == 10*ones(1, 2)
     @test Dense(10, 2, identity, initW = ones, initb = zeros)(ones(10,1)) == 10*ones(2, 1)
     @test Dense(10, 2, identity, initW = ones, initb = zeros)([ones(10,1) 2*ones(10,1)]) == [10 20; 10 20]
-
   end
 
   @testset "Diagonal" begin