Peder Holt <peder.holt <at> gmail.com> writes:
I vote to accept BOOST_SCOPE_EXIT. Thanks.
The library complements scope guard in the same way as BOOST_FOREACH complements std::for_each. Both of them has a place, and it depends on the users preferences what they will use. I prefer BOOST_SCOPE_EXIT.
This is a good analogy, I like it.
I would wish for a syntax more in line with BOOST_FOREACH (omitting the BOOST_SCOPE_EXIT_END, but the best I've been able to come up with is: {BOOST_SCOPE_EXIT( (commit)(m_persons) ) { if(!commit) m_persons.pop_back(); } };
Previous version of the library implemented the macro this way but it looked too rubyish. In Ruby, a typical block look like this { |commit, m_persons| # Warning: next two lines are C++, not Ruby! if(!commit) m_persons.pop_back(); }
With the leading open clause, this is not exactly an improvement...
I too miss the BOOST_LOCAL_FUNCTION_DEF macro. This should be a part of the library before it is included in boost.
I would say, it should be a separate library that integrates nicely with ScopeExit.
One possible implementation is:
...
which expands to: int i=5; int j=4; int (*function_ref)()=0; typedef BOOST_TYPEOF(i) type_0; typedef BOOST_TYPEOF(j) type_1; typedef BOOST_TYPEOF(function_ref()) return_type_1; struct name_impl { type_0& i; type_1& j; name_impl(type_0& i_,type_1& j_) : i(i_),j(j_) {} return_type_1 operator()(int x,int y) { i=x;j=y; return i+j; } } name(i,j); //...
name(5,6);
There is one fundumental problem with this: name_impl is a local structure and cannot be used in templates. int result = accumulate(begin, end, 0, name); // Compilation error!
When it comes to handle references or copies of arguments, I think the following can be made to work: int BOOST_LOCAL_FUNCTION_DEF(name,ref(i)const_ref(j)(k))(int x,int y) If not, the following can be made to work by using BOOST_PP_IS_UNARY. ( (const&)(i) ) ( j ), but this is starting to look like lisp.
'rref(i)const_ref(j)' looks good. I didn't think of const_ref before. These names should be consistent with reference_wrapper helper functions: ref and cref. Passing by value can be either without any prefix (as you suggest) or with the 'val' prefix. -- Alexander