Make object deep-copying fallible to avoid having to implement it for the...

Make object deep-copying fallible to avoid having to implement it for the whole Stream class hierarchy
6 jobs for memoize-fetch in 4 minutes and 27 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #436222
build

00:04:26

passed #436227
build_android

00:01:00

passed #436223
build_clang_libcpp

00:04:27

passed #436226
build_clazy

00:04:23

passed #436225
build_mingw64_fedora

00:04:07

passed #436224
build_ubuntu_16_04

00:01:47