No, in fact the way with externally linked static strings is valid and
works. However it is a bit clumsy...
-Marten
Quoting David Bronke <[EMAIL PROTECTED]>:
> The problem with string literals extends to variables as well, i
> believe. AFAIK, the only things valid for a template's arguments are
> type or class names. (not variables, objects, or literals of any type)
> This causes some problems for a few of the methods mentioned below,
> with the exception of the macro-based one.
>
> Dave
>
> On 6/17/06, Michael D. Adams <[EMAIL PROTECTED]> wrote:
>> On 6/17/06, Marten Svanfeldt <[EMAIL PROTECTED]> wrote:
>> > Hi,
>> >
>> > Intresting idea, and it would be nice if it worked. However there are
>> > a few problems with it,
>> >
>> > Quoting "Michael D. Adams" <[EMAIL PROTECTED]>:
>> >
>> > > template<char* name> class csNullEventHandlerNames0 { ... };
>> > > template<char* name, typename T1> class csNullEventHandlerNames1 :
>> > > public T1 { ... };
>> > >
>> > > These would be used as follows.
>> > >
>> > > class csFoo : public
>> > > csNullEventHanderNames0<"crystalspace.module.name"> { ... };
>> > > class csBar : public
>> > > csNullEventHanderNames1<"crystalspace.module.name"> { ... };
>> >
>> > Unfortunatly this is not legal C++. You cannot specialize a char*
>> > template parameter with a string literal. This is the only reason we
>> > still use a macro for SCF_INTERFACE and SCF_FACTORY.
>> >
>> > Given that this part breaks down I don't see how the rest of the
>> > proposal can work properly, unfortunatly.
>>
>> I hadn't known that about C++, but I did some research and what you
>> say is correct.
>>
>> I've been trying to think of alternatives that achieve the same effect
>> with different mechanisms. None of them are great, but I'll present
>> them here. Maybe they will spark some ideas or someone can refine
>> them.
>>
>> We could instantiate the template with a string *variable* instead of
>> a literal, but that probably wouldn't buy us very much. (The variable
>> would need to have external linkage to keep the compiler happy about
>> using it as template argument.)
>>
>> extern const char foo [] = "crystalspace.module.name";
>> class csFoo : public csNullEventHandlerNames0<foo> { ... };
>>
>> We could pass the string as argument to the constructor. This assumes
>> that all event handlers are used as instiantiated objects and not as
>> static classes. It might also pose a maintinance problem to keep
>> multiple constructors in sync.
>>
>> class csFoo : public csNullEventHandlerNames0 {
>> csFoo () : csNullEventHandlerNames0("crystalspace.module.name") { ... }
>> ... };
>>
>> We could reduce the macro down to a type trait that contains the
>> string. This would have just as many "magic" places as before though
>> the magic would be "smaller magic".
>>
>> #define CS_EVENT_HANDLER_NAME(x) \
>> struct EventHandlerTraits { \
>> static const char* GetName() { return x; } \
>> }
>> class csFoo : public csNullEventHandlerNames0<csFoo> {
>> CS_EVENT_HANDLER_NAME("crystalspace.module.name");
>> ...
>> };
>>
>> We could pass a csEventID as template argument instead of a string.
>> This option is probably impossible as it would require partially
>> populating the event name registry object at compile time.
>>
>> Brainstorming,
>> Michael D. Adams
>> [EMAIL PROTECTED]
>>
>>
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