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Subject: [boost] [function] "paranoia" vs efficiency
From: Domagoj Saric (domagoj.saric_at_[hidden])
Date: 2009-10-02 07:20:23

As far as I can see boost::function<>::operator() performs:
if (this->empty())
before invoking the stored function (object)...
My question is why or why only this "checked"/"safe" approach/method of
invocation exists?
Because this:
 - causes (extra) code branching
 - causes the compiler to insert exception throwing and handling code in
surrounding/calling code (which need not otherwise be if the function stored
in the boost function instance is itself nothrow)
 - inserts a call to the bad_function_call constructor
 - disables the compiler from inlining the function (MSVC atleast)
 - disables NVRO (MSVC atleast, )
while at the same time I would most often consider calling a
"null-function-pointer" a programmer error (that would therefor need to be
"handled" with an assert not an exception), not a runtime 'unpredictable'

...IMO the default should be not to include this check (i.e. use an assert)
and provide a safeInvoke() type of method for those users and cases that
actually require/want this type of check/behaviour...
...or atleast "it would be welcomed" if a non-checking unsafeInvoke() type
of method would be provided for those that are 'sure' that the
boost::function<> object is valid (for example in the line before i've just
performed the same check to decide whether to call the function object or

 "That men do not learn very much from the lessons of history is the most
important of all the lessons of history."
 Aldous Huxley 

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