template class question (more elegant soln)

[Anonymous]

I want to be able to restrict the set of classes for which a template
class can be instantiated (i.e enforce that all instantiation MUST be
for classes taht derive from a base type BaseType).

This occured to me immediately, but use of a dummy variable is not
elegant - are there other (more elegant) ways of doing this?
template <class DerivedType>
class MyClass
{
public:
MyClass():m_type(*DerivedType){};
~MyClass(){}

private:
BaseType * m_type ; //dummy variable
};

[Victor Bazarov]

Anonymous wrote:

I want to be able to restrict the set of classes for which a template
class can be instantiated (i.e enforce that all instantiation MUST be
for classes taht derive from a base type BaseType).

This occured to me immediately, but use of a dummy variable is not
elegant - are there other (more elegant) ways of doing this?
template <class DerivedType>
class MyClass
{
public:
MyClass():m_type(*DerivedType){};
~MyClass(){}

private:
BaseType * m_type ; //dummy variable
};

The combination of 'Boost::enable_if' with 'base_or_derived' temlplate
helpers should essentially do what you ask, I think.

V
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[Gianni Mariani]

Anonymous wrote:

I want to be able to restrict the set of classes for which a template
class can be instantiated (i.e enforce that all instantiation MUST be
for classes taht derive from a base type BaseType).

This occured to me immediately, but use of a dummy variable is not
elegant - are there other (more elegant) ways of doing this?
template <class DerivedType>
class MyClass
{
public:
MyClass():m_type(*DerivedType){};
~MyClass(){}

private:
BaseType * m_type ; //dummy variable
};

Something like this would be better:
template <class DerivedType>
class MyClass
{
static_assert(is_derived(DerivedType,BaseType));
public:
MyClass()
{}

private:
BaseType * m_type ; //dummy variable
};

I have not used them but I think you'll find static_assert and
is_derived in boost.

[Robi-Wan-Kenobi]

I am asking myself why do you want to do that?
I think in that case a template is not needed at all. You can make a
class that's holding a pointer (or more of them) to your BaseType as
an aggregation and you can assign any derivedType to that (these)
pointer(s).
But maybe you can explain why you need a template here.

Greetings