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: Peter Myerscough-Jackopson (peter.myerscough-jackopson_at_[hidden])
Date: 2010-09-06 12:03:31

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. 

 

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()].

 

 

Peter

 

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