julia> immutable Foo{T} end

julia> stagedfunction bar{T}(x::Foo{T})
         return :(Foo{$T}())
       end
bar (generic function with 1 method)

julia> @code_warntype bar(Foo{(1,2)}())
Variables:
  x::Foo{(1,2)}

Body:
  begin
      return ((top(apply_type))(Foo,(1,2))::Type{_<:Foo{T}})()::Foo{T}
  end::Foo{T}