use 5-arg copyto

src/destructure.jl

@@ -152,14 +152,18 @@ end
 function _rebuild!(x, off, flat::AbstractVector, len = length(flat); walk = _Trainable_biwalk(), kw...)
   len == length(flat) || throw(DimensionMismatch("Rebuild expected a vector of length $len, got $(length(flat))"))
   fmap(x, off; exclude = isnumeric, walk, kw...) do y, o
-    copyto!(y, _getat(y, o, flat, view))
+    # copyto!(y, _getat_view(y, o, flat))
+    copyto!(y, 1, flat, o+1, length(y))
   end
   x
 end
 
-_getat(y::Number, o::Int, flat::AbstractVector, _...) = ProjectTo(y)(flat[o + 1])
-_getat(y::AbstractArray, o::Int, flat::AbstractVector, get=getindex) =
-  ProjectTo(y)(reshape(get(flat, o .+ (1:length(y))), axes(y)))  # ProjectTo is just correcting eltypes
+_getat(y::Number, o::Int, flat::AbstractVector) = ProjectTo(y)(flat[o + 1])
+_getat(y::AbstractArray, o::Int, flat::AbstractVector) =
+   ProjectTo(y)(reshape(flat[o .+ (1:length(y))], axes(y)))  # ProjectTo is just correcting eltypes
+
+# _getat_view(y::AbstractArray, o::Int, flat::AbstractVector) =
+#   view(flat, o .+ (1:length(y)))
 
 struct _Trainable_biwalk <: AbstractWalk end