Classes with the same functionality but not convertible

[Tom Howard]

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Hi,

On a project I'm working on we need a few of ID classes for various sub
systems. Each ID class (e.g. EntityID, ClassID, PhysicsID, AnimationID)
does exactly the same thing, but we would like to prevent conversion
from different types of IDs (e.g. boost::is_convertible< EntityID,
ClassID >::value is false), to avoid stupid errors.

So far we have come up with to methods for achieving this.

Method 1:

Create a macro called ORG_CREATE_ID_TYPE which takes a class name as an
argument, then when you need a new ID class, you just include the header
where the macro is defined and add

ORG_CREATE_ID_TYPE( MyID )

where you need MyID defined

Method 2:

enum IDTag { EntityIDTag, ClassIDTag, ..., MyIDTag };

template< IDTag T >
class BaseID
{
....
};

typedef BaseID< EntityIDTag > EntityID;
typedef BaseID< ClassIDTag > ClassID;
....
typedef BaseID< MyIDTag > MyID;

The template method is preferred but it is 17% slower to compile, which
given the size of the project and the number of developers is going to
add up to too much time over the next couple of years.

Is there another option I'm overlooking or some techniques you can think
of to make the template method faster?

Thanks in advance.

Cheers,

Tom Howard
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[Shezan Baig]

Tom Howard wrote:

Create a macro called ORG_CREATE_ID_TYPE which takes a class name as an argument, then when you need a new ID class, you just include the header where the macro is defined and add

ORG_CREATE_ID_TYPE( MyID )

What does this macro do?

[davidrubin]

Shezan Baig wrote:

Tom Howard wrote:

Create a macro called ORG_CREATE_ID_TYPE which takes a class name

as an

argument, then when you need a new ID class, you just include the

header

where the macro is defined and add

ORG_CREATE_ID_TYPE( MyID )

What does this macro do?

Probably something along the lines of

#define ORG_CREATE_ID_TYPE(MyID) \
struct #MyID { \
//... \
}

Another option you should consider is a script (e.g., Perl) that
generates new ID-type components. This should reduce the burden on your
compiler. /david

[Tom Howard]

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Shezan Baig wrote:

Tom Howard wrote:

Create a macro called ORG_CREATE_ID_TYPE which takes a class name as

an

argument, then when you need a new ID class, you just include the

header

where the macro is defined and add

ORG_CREATE_ID_TYPE( MyID )

What does this macro do?

#define ORG_CREATE_ID_TYPE( id_name ) \
class id_name \
{ \
....
};

It does the trick, but we would like to avoid the macro usage if
possible. One of the reasons being that Intellisense in VC++ doesn't
play with the macro generated classes.

Templates are logically the way to go, because with templates each id
class is an instance of the id template which is conceptually exactly
what we want, however we can't find a way to overcome the speed hiccup.

Cheers,

Tom Howard
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