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From: Jesse Jones (jesjones_at_[hidden])
Date: 2001-06-13 07:32:55

I have some quibbles with the design, but I've found this sort of
callback library awfully useful and the code looks fundamentally
sound so I think it should be accepted into boost. I tested it with
CodeWarrior 6.1 on the Mac and the only problems I ran into were some
niggling little details because I had the warnings cranked up (see

There are a few design decisions that I'm dubious about:

1) I don't see why policies and mixins should be built into function.
I think the way to handle this is sort of like the way argument
binding is handled: clients would call a binder function with the
function and the pre/post functions and a boost::function would be
returned that points to an appropriate function object.

2) I'd prefer it if calling a function with an empty target was
treated as a precondition violation (and handled with an assert). The
rule of thumb that most people seemed to buy into was that asserts
should be used where clients can easily preflight and exceptions

3) In the absence of a bind library it seems silly to force everyone
to generate their own copies of the bind code in the FAQ. I would
imagine that nearly everyone who uses boost::function is going to
need to work with methods so I think their should be a stopgap
solution inside boost.

I added some new tests to function_test.cpp. At the top I added a
couple of new functions:

static int do_stuff(int n = 0) {(void) n; return 0;}
static int write_return_three() { global_int = 3; return 3;}

And in test_zero_args() I added some code:

   // Use default argument
   function<int> d(do_stuff);
   BOOST_TEST(d() == 0);

   // Test compatible return types
   function<long> l(generate_five);
   BOOST_TEST(l() == 5);

   // Ignore return values
   function<void> i(write_return_three);
   global_int = 0;
   BOOST_TEST(global_int == 3);

   // Test const function's
   const function<int> c(generate_five);
   BOOST_TEST(c() == 5);

Here are the changes I had to make to get the code past the compiler:

1) There are signed/unsigned conversion problems in
allocator_test.cpp: I changed the allocate and deallocate methods so
they take a std::size_t instead of an int.

2) In catch_exceptions.hpp I made report_exception() inline (static
would work just as well).

3) In defarg_test.cpp I made test_two_args() static.

4) In function_test.cpp I made test_zero_args(), test_one_arg(),
test_two_args(), and test_emptiness() static.

5) In test_main.cpp I made report_error() and report_critical_error() static.

6) I undef'ed nil at the top of function_base.hpp, but as was
mentioned this isn't going to work in the real world.

   -- Jesse

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