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Function template type inference doesn't work with inheritan

 
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Guest
PostPosted: Sun May 13, 2007 9:11 am    Post subject: Function template type inference doesn't work with inheritan Reply with quote


I'm having a problem getting derived types to be inferred as valid
parameters by a function template.

template <typename T>
struct Base {}

template<typename T>
struct Derived : public Base<T> {}

template <typename T>
void fn(Base<T>* b) { }

When I call fn with a Derived<int>* gcc gives me the error "no
matching function for call to..."
Is there any way to get the function template to accept derived
objects?

Thanks,
Alex Rubinsteyn
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Gianni Mariani
Guest
PostPosted: Sun May 13, 2007 9:11 am    Post subject: Re: Function template type inference doesn't work with inher Reply with quote


On May 13, 4:50 pm, MikhailGorbac...@gmail.com wrote:
Quote:
I'm having a problem getting derived types to be inferred as valid
parameters by a function template.

template <typename T
struct Base {}

template<typename T
struct Derived : public Base<T> {}

template <typename T
void fn(Base<T>* b) { }

// strictly not want you want but might do
template <typename X>
void fn(X* x)
{
Base<T>* b( x );
....
}

Or add this method - at least you know that it's only the derived ones
that you're getting

template <typename T>
void fn(Derived<T>* x)
{
Base<T> * b = x;
fn( b );
}


Or - hack but does the job - breaks some non-compliant compilers

// strictly not want you want but might do
template <typename X>
void fn(X* x, Convertible<X *, Base<T> *>::type = 0 )
{
Base<T>* b( x );
fn(b);
}

where Convertible is a special template class to determine if the type
of X is one of the types you allow be used - it's probably overkill
for this case.

Quote:

When I call fn with a Derived<int>* gcc gives me the error "no
matching function for call to..."
Is there any way to get the function template to accept derived
objects?

Thanks,
Alex Rubinsteyn
Back to top
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