Re: [boost] Domagoj Saric: "Re: [function] invoking without requiring boost::throw_exception"

Subject: Re: [boost] Domagoj Saric: "Re: [function] invoking without requiring boost::throw_exception"
From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2010-09-06 23:55:31

On Mon, Sep 6, 2010 at 12:03 PM, Peter Myerscough-Jackopson
<peter.myerscough-jackopson_at_[hidden]> wrote:
> From: "Peter Myerscough-Jackopson" <peter.myerscough-jackopson_at_[hidden]>
> Sent: Thursday, September 02, 2010 5:36 PM
>> I am using boost::function on an embedded platform, which requires me to
>> not use exceptions, and as commented in the thread associated with
>>
>> http://article.gmane.org/gmane.comp.lib.boost.devel/195351
>>
>> I am checking that the function object contains a function before
>> calling it. There is therefore no need for the invocation of the
>> function to check if it is valid, but also there is no method circumvent
>> this checking, and therefore my program requires the definition of
>> boost::throw_exception, when really it is not needed. This is a concern
>> because I intend on compiling my code into a library and do not wish to
>> require the user to define boost::throw_exception, especially when I am
>> guaranteeing it isn't going to be called from this site. I liked the
>> idea of a templated NOP for the function library, but at the very least
>> an unchecked invocation method would be great, or a nop-if-empty
>> invocation method would be useful.
>
> If you are certain that neither you nor your users use or will use
> boost::throw_exception (to actually handle some other cases 'exceptional'
> cases in other parts of boost) then you can provide the definition yourself.
>
>
>
> I cannot know whether my users will invoke other parts of boost that may make use of boost::throw_exception because my code is being compiled up and provided as a (application support) library. Also, since I know that I will never call the function object when it is null, I don’t want to burden my users by requiring them to define a function that will never be called from my code. As it is currently I am resorting to mimicking the code that occurs after the check and I have put a check in to ensure the library is compiled with an exact version of boost, a poor/bad/nightmare work around, but it means my users don’t have to define throw_exception.

I don't understand why you say your users need to define
boost::throw_exception. If BOOST_NO_EXCEPTIONS is not defined, then
the Boost Exceptions library defines throw_exception. If you define
BOOST_NO_EXCEPTIONS, then you, not your users, need to define
throw_exception.

http://www.boost.org/doc/libs/1_44_0/libs/exception/doc/throw_exception.html

It seems to me that in your situation on an embedded platform without
exception support, you should define BOOST_NO_EXCEPTIONS and then use
something like Domagoj's example of an unreachable throw_exception
implementation.

>
> As others have noted, a common idiom for using a boost function object is to check if it is non-empty prior to calling it, is it an unreasonable extension to add this call? I am aware TR1 has subsumed “function” and so it is probably not possible remove the if-clause, but adding an unchecked invoke has significant benefits, [unchecked_invoke(), might be a better name than purely invoke()].

Yeah, it seems like a good idea to add something like this. Could you
submit a feature request at svn.boost.org, if there isn't one there
already?

Daniel Walker