return Params from params

src/tracker/back.jl

@@ -66,15 +66,28 @@ end
 # Out-of-place gradients
 
 struct Params
-  params::IdSet
-  Params(xs) = new(IdSet(xs))
+  order::Vector{Any}
+  params::IdSet{Any}
+  Params() = new([], IdSet())
 end
 
-@forward Params.params Base.iterate, Base.length
+@forward Params.order Base.iterate, Base.length
+
+function Base.push!(ps::Params, x)
+  if !(x in ps.params)
+    push!(ps.order, x)
+    push!(ps.params, x)
+  end
+  return ps
+end
+
+Base.push!(ps::Params, x...) = (foreach(x -> push!(ps, x), x); ps)
+
+Params(xs) = push!(Params(), xs...)
 
 function Base.show(io::IO, ps::Params)
   print(io, "Params([")
-  join(io, ps.params, ", ")
+  join(io, ps.order, ", ")
   print(io, "])")
 end
 

src/tracker/idset.jl

@@ -7,6 +7,7 @@ Base.eltype(::IdSet{T}) where T = T
 
 IdSet() = IdSet{Any}()
 
+Base.push!(s::IdSet) = s
 Base.push!(s::IdSet{T}, x::T) where T = (s.dict[x] = nothing; s)
 Base.delete!(s::IdSet{T}, x::T) where T = (delete!(s.dict, x); s)
 Base.in(x, s::IdSet) = haskey(s.dict, x)

src/treelike.jl

@@ -40,7 +40,7 @@ function prefor(f, x; seen = IdSet())
 end
 
 function params(m)
-  ps = []
+  ps = Params()
   prefor(p ->
     Tracker.istracked(p) && Tracker.isleaf(p) &&
       !any(p′ -> p′ === p, ps) && push!(ps, p),