On Tue, Aug 21, 2012 at 4:47 PM, Alex Rousskov
<rouss...@measurement-factory.com> wrote:
> On 08/21/2012 12:19 AM, Kinkie wrote:
>>> .h file:
>>> > #if OPTIONAL_FEATURE
>>> > extern void someFunction();
>>> > #else
>>> > // #define someFunction() // NOP
>>> > // or:
>>> > // static inline someFunction() {/* NOP */}
>>> >
>>> > #endif
>>> >
>>> > .cc file:
>>> > #if OPTIONAL_FEATURE
>>> > void someFunction()
>>> > {
>>> > //code
>>> > }
>>> > #endif
>>> >
>>> > client code:
>>> > someFunction(arg);
>> If any, I'd go for static inline (or just inline, after all the
>> namespace is already polluted).
>> Is the cost of the extra function call worth the decreased readibility?
>
> No statics or #defines in headers unless really necessary, please.
>
> Use inline. Inline has the same effect on the namespace as static but
> the call to an [empty] inline function is more likely to be removed by
> the compiler. If done right, there will be no runtime cost in most cases.
>
> Please be careful about function arguments though. They or related
> conversion operators are sometimes unavailable outside of
> OPTIONAL_FEATURE protection.
>
> You may have to create a shadow hierarchy of types and names to use this
> approach in some cases (some recent Squid code does things like that;
> see src/ipc/AtomicWord.h, for example).
>
> This NullObject-like approach works best for commonly used things. If we
> are talking about a single obscure function call which requires
> #inclusion of a complex header, then it may be best to leave it (and its
> #include) inside #ifdef guards to minimize complications.
I'm thinkin about applying some judgement and the Pareto principle: if
we can reduce 80% of #if USE_STUFF we have got a good result already.
For instance:
in protos.h
#if USE_WCCP
void wccpInit(void);
#endif
in wccp.cc
#if USE_WCCP
// stuff
void
wccpInit(void)
{
// code
}
// stuff
#endif
in main.cc:
#if USE_WCCP
wccpInit();
#endif
This is a very simple example, and also a very typical one.
I'd like to turn it into:
wccp.h:
/** initialize wccp
* \note it's a NOP unless USE_WCCP is defined
*/
void wccpInit(void);
wccp.cc:
#if USE_WCCP
// stuff
void
wccpInit(void)
{
// code
}
// stuff
#else
void wccpint(void) {}
#endif
main.cc:
wccpinit();
Alternatively (less readability and less runtime overhead),
wccp.h:
#if USE_WCCP
void wccpInit(void);
#else
inline void wccpInit(void) {}
#endif
//everything else as previous example
// but in this case, where do we put doxyigen-docs? Before the #if USE_WCCP?
For more complex stuff, I'd live as is; the tradeoff of readability
vs. problems arising from code duplication is this case riskier.
--
/kinkie
