On Tue, Nov 2, 2010 at 1:17 AM, Emil Dotchevski <emil@revergestudios.com> wrote:
On Mon, Nov 1, 2010 at 8:58 PM, OvermindDL1 <overminddl1@gmail.com> wrote:
f(unsafe_no_throw,1); // possible new syntax, calls function, no null check u(unsafe_no_throw,1); // possible new syntax, whatever the platform
This is somewhat redundant since you can already do
assert(f); f(1);
I was proposing a similar change, to add a boost::function constructor that takes std::nothrow_t, which can be used to initialize an empty function object which asserts and doesn't throw upon calling op(). However I'm not sure there is a use case even for this: it lets you pick throw or no-throw semantics, but no-throw semantics are only useful in BOOST_NO_EXCEPTIONS builds, and therefore the global no-throw behavior supported by boost::throw_exception should be sufficient.
With a smart enough optimizer, that should indeed remove the `if` check (my purpose of this), but that then adds an assert in the code that will still get run at runtime. The problem with adding a nothrow_t in the constructor is that state then needs to be held (or you need to templately-branch based on it, which would remove the runtime state requirement, but that is a lot of extra code to manage), but there are some places in code where calling a boost::function may very well possibly be null, and an exception may be warranted (like outside of my code), but other places (like inside of my code) I already know before-hand whether or not a function is null or not and whether or not to call it, even if I have no `if` check before its call, just based on how the program flow works. I just want it to call it, potentially inline it (which I have seen the optimizer do nicely enough), with no dang checks getting in the way. The called function might still throw, might not, who knows, I just do not want the check, and yes I have a use-case for it in tight loops (where currently a fastdelegate outperforms the identical code using boost::function by a rather healthy margin, and looking at the assembly, the only difference is the `if` check).