Re: Lambda Expression + RAII = The landscape of exception-safe programming will change in C++09!

From:

ymett <ymett.on.usenet@gmail.com>

Newsgroups:

comp.std.c++

Date:

Mon, 24 Sep 2007 11:24:52 CST

Message-ID:

<1190650571.059596.222230@y42g2000hsy.googlegroups.com>

On Sep 24, 6:42 pm, pongba <pon...@gmail.com> wrote:

Exception-safe Programming is hard, but a scope(exit) facility like
that of D language can ease the task. Now it is difficult in C++03 to
implement a easy to use one (http://194.6.223.221/~nasonov/
scope_exit-0.04/libs/scope_exit/doc/html/index.html).

With C++09 coming, we can except that a much more elegant solution is
on the horizon!

Check the code below:

class ScopeExit
{
public:
ScopeExit(tr1::function<void()> func) : func_(func) { }
~ScopeExit() { func_(); }
private:
tr1::function<void()> func_;

};

#define BOOST_SCOPE_EXIT(expr) \
ScopeExit scope_exit_##__LINE__(expr)

The cost of using tr1::function (to be std::function in C++09) can be
avoided:

template<class F>
class ScopeExit
{
public:
   ScopeExit(F func) : func_(func) { }
   ~ScopeExit() { func_(); }
private:
   F func_;
};

template<class F>
ScopeExit<F> make_ScopeExit(F func)
{
   return ScopeExit<F>(func);
}

#define BOOST_SCOPE_EXIT(expr) \
   auto scope_exit_##__LINE__(make_ScopeExit(expr))

// use case
void f()
{
bool commit = false;
account1.draw(10);
BOOST_SCOPE_EXIT((
  <&>(){
    if(!commit)
      account1.deposit(10);
  }
)); // lambda expression - see proposal N2413
account2.deposit(10);
commit = true;

}

Usage unchanged.

Yechezkel Mett

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