use array to define Zeros

src/utils.jl

@@ -163,16 +163,39 @@ julia> bias = Conv((2,2), 1=>3, bias = Flux.Zeros())
 Conv((2, 2), 1=>3)
 ```
 """
-struct Zeros <: Number end
+struct Zeros{T,N} <: AbstractArray{T,N}
-for f in (:+, :-)
+  size::Tuple
- @eval $f(a::Union{Number, Zeros}, b::Zeros) = a
 end
-Base.:*(a::Union{Number, Zeros}, b::Zeros) = zero(a)
+
+Zeros(::Type{T}, sz...) where T = Zeros{T,length(sz)}(sz)
+Zeros(sz::Integer...) = Zeros(Bool, sz...)
+
++(a::Union{AbstractVecOrMat, Number}, ::Zeros) = a
+
+Base.size(xs::Zeros) = xs.size
+Base.IndexStyle(::Type{<:Zeros}) = IndexLinear()
+
+Base.axes(xs::Zeros) = Base.OneTo.(size(xs))
+
+Base.getindex(xs::Zeros{T,N}, i::Int) where {T,N} = zero(T)
+Base.setindex(xs::Zeros, args...) =
+  error("setindex disallowed on Zeros Array")
+Base.setindex!(xs::Zeros, args...) =
+  error("setindex! disallowed on Zeros Array")
+
+Base.collect(xs::Zeros{T,N}) where {T,N} = fill(zero(T), size(xs))
+
+@adjoint reshape(xs::Zeros{T}, dims...) where T =
+  reshape(xs, dims...), _ -> nothing
+
+for f in (:+, :-)
+ @eval $f(a::Union{AbstractArray{<:Number}, Zeros}, b::Zeros) = a
+end
+Base.:*(a::Union{AbstractArray{<:Number}, Zeros}, b::Zeros) = zero(a)
 
 broadcasted(::typeof(+), arr::AbstractArray, ::Zeros) = arr
+broadcasted(::typeof(-), arr::AbstractArray, ::Zeros) = arr
 broadcasted(::typeof(*), arr::AbstractArray, ::Zeros) = zero(arr)
-Base.reshape(xs::Zeros, args...) = xs
-@adjoint reshape(xs::Zeros, dims...) = reshape(xs, dims...), _ -> nothing
 
 """
     @jit ...