[libcxx] guard throw with exception enabling check

[weimingz]

Summary

this fixes build error when built with c++14 and no exceptions

[rmaprath]

That looks fine to me.

[grandinj]

include/experimental/optional

524 ↗

(On Diff #61755)

If this kind of code is going to show up in lots of places, then maybe wrap it up in a macro:

_LIBCPP_THROW_OR_ASSERT(bad_optional_access(), "bad optional access")

?

With some extra preprocessor magic, and if LLVM didn't care about the string in the assert, could even leave out the second parameter

[rmaprath]

include/experimental/optional

524 ↗

(On Diff #61755)

In D14653 (which did not land), I had used a _LIBCPP_THROW macro for a similar purpose (see changes in config/include). Currently there is no uniform mechanism adopted in the library for throwing exceptions.

I agree that it would be nice to fix this. I will revive that part of D14653 soon.

Thanks for the reminder!

[weimingz]

It's a good idea. Currently, there are about 600+ "throws" being
guarded by _LIBCPP_NO_EXCEPTIONS macro.

How about let's merge the patch now and I can do the conversion of
existing code to the wrapper in background?

Weiming

[rmaprath]

In D21673#466544, @weimingz wrote:

It's a good idea. Currently, there are about 600+ "throws" being
guarded by _LIBCPP_NO_EXCEPTIONS macro.

How about let's merge the patch now and I can do the conversion of
existing code to the wrapper in background?

Weiming

Sounds good to me.

Thanks!

[mclow.lists]

Just a reminder - the people who can approve patches for libc++ are @mclow.lists and @EricWF.

[rmaprath]

In D21673#467317, @mclow.lists wrote:

Just a reminder - the people who can approve patches for libc++ are @mclow.lists and @EricWF.

My bad, I thought it was too trivial. Won't happen again :)

/ Asiri

libcxx/trunk/include/experimental/optional

public:
 
     _LIBCPP_INLINE_VISIBILITY
     constexpr explicit operator bool() const noexcept {return this->__engaged_;}
 
     _LIBCPP_INLINE_VISIBILITY
     constexpr value_type const& value() const
     {
         if (!this->__engaged_)
+#ifndef _LIBCPP_NO_EXCEPTIONS
             throw bad_optional_access();
+#else
+            assert(!"bad optional access");
+#endif
         return this->__val_;
     }
 
     _LIBCPP_INLINE_VISIBILITY
     value_type& value()
     {
         if (!this->__engaged_)
+#ifndef _LIBCPP_NO_EXCEPTIONS
             throw bad_optional_access();
+#else
+            assert(!"bad optional access");
+#endif
         return this->__val_;
     }
 
     template <class _Up>
     _LIBCPP_INLINE_VISIBILITY
     constexpr value_type value_or(_Up&& __v) const&
     {
         static_assert(is_copy_constructible<value_type>::value,