googletest-param-test-test.cc:502:8: error:
definition of implicit copy constructor for
'NonDefaultConstructAssignString' is deprecated because it has a
user-declared copy assignment operator [-Werror,-Wdeprecated]
void operator=(const NonDefaultConstructAssignString&);
^
googletest-port-test.cc:97:11: error:
definition of implicit copy constructor for 'Base' is deprecated because
it has a user-declared destructor [-Werror,-Wdeprecated]
virtual ~Base() {}
^
gmock-spec-builders.h:503:3: error:
definition of implicit copy constructor for 'Expectation' is deprecated
because it has a user-declared destructor [-Werror,-Wdeprecated]
~Expectation();
^
None of these are strictly needed for correctness.
A large number of them (maybe all of them?) trigger `-Wdeprecated`
warnings on Clang trunk as soon as you try to use the implicitly
defaulted (but deprecated) copy constructor of a class that has
deleted its copy assignment operator.
By declaring a deleted copy assignment operator, the old code
also caused the move constructor and move assignment operator
to be non-declared. This means that the old code never got move
semantics -- "move-construction" would simply call the defaulted
(but deprecated) copy constructor instead. With the new code,
"move-construction" calls the defaulted move constructor, which
I believe is what we want to happen. So this is a runtime
performance optimization.
Unfortunately we can't yet physically remove the definitions
of these macros from gtest-port.h, because they are being used
by other code internally at Google (according to zhangxy988).
But no new uses should be added going forward.
We are about to remove all uses of GTEST_DISALLOW_ASSIGN_ in favor
of using the Rule of Zero everywhere.
Unfortunately, if we use the Rule of Zero here, then when the compiler
needs to figure out if VariadicMatcher is move-constructible, it will
recurse down into `tuple<Args...>`, which on libstdc++ recurses too deeply.
In file included from googlemock/test/gmock-matchers_test.cc:43:
In file included from googlemock/include/gmock/gmock-matchers.h:258:
In file included from /usr/include/c++/5.5.0/algorithm:60:
In file included from /usr/include/c++/5.5.0/utility:70:
In file included from /usr/include/c++/5.5.0/bits/stl_pair.h:59:
In file included from /usr/include/c++/5.5.0/bits/move.h:57:
/usr/bin/include/c++/5.5.0/type_traits:115:26: fatal error:
recursive template instantiation exceeded maximum depth of 256
: public conditional<_B1::value, _B1, _B2>::type
^
The move constructor is the only problematic case, for some unknown reason.
With GTEST_DISALLOW_ASSIGN_, the presence of a copy assignment operator
causes the move constructor to be non-declared, thus non-defaulted, thus
non-problematic. Without GTEST_DISALLOW_ASSIGN_, we have to do one of the
following:
- Default the copy constructor, so that the move constructor will be non-declared.
- Define our own non-defaulted move constructor.
...except that doing the latter STILL did not work!
Fortunately, the former (default the copy constructor, don't provide
any move constructor) both works in practice and is semantically
equivalent to the old code.
Arthur O'Dwyer