template question using named constructor

[bob holder]

Hi folks, I have a question. Can I use a named constructor with templates?
If yes I am not sure the syntax. For example:

template <size_t N> class ABC {

public:
typedef ABC<N> *handle;

static handle create(size_t s) { return new ABC<s>(); }

private:
ABC();
};

main () {
ABC<5>::handle my_abc;

my_abc = ABC<5>.create(5); // compile error this line
}

I need to control the construction process, hence the need to hide the
default ctor.

thanks,
bob

[John Harrison]

"bob holder" <holder25AThotmailDOTcom> wrote in message
news:Hw********@news.boeing.com...

Hi folks, I have a question. Can I use a named constructor with templates?
If yes I am not sure the syntax. For example:

template <size_t N> class ABC {

public:
typedef ABC<N> *handle;

static handle create(size_t s) { return new ABC<s>(); }

private:
ABC();
};

main () {
ABC<5>::handle my_abc;

my_abc = ABC<5>.create(5); // compile error this line
}

I need to control the construction process, hence the need to hide the
default ctor.

thanks,
bob

Like this

template <size_t N> class ABC
{
public:
typedef ABC<N> *handle;
static handle create() { return new ABC<N>(); }
};

int main ()
{
ABC<5>::handle my_abc;

my_abc = ABC<5>::create();
}

john

[Claudio Jolowicz]

On Wed, 21 Apr 2004, John Harrison wrote:

"bob holder" <holder25AThotmailDOTcom> wrote in message
news:Hw********@news.boeing.com...

Hi folks, I have a question. Can I use a named constructor with templates?
If yes I am not sure the syntax. For example:

[snip]
I need to control the construction process, hence the need to hide the
default ctor.

thanks,
bob

Like this

#include <cstdlib>
template <size_t N> class ABC
{
public:
typedef ABC<N> *handle;
static handle create() { return new ABC<N>(); }
private: //I think you forgot this bit
ABC() {/*whatever*/}
};

int main ()
{
ABC<5>::handle my_abc;

my_abc = ABC<5>::create();
}

Bob, do you really want to use a template here? The obvious solution
would have been:

class ABC
{
public:
ABC(size_t);
};

This automatically hides the default constructor.

--
Claudio Jolowicz
http://www.doc.ic.ac.uk/~cj603

[bob holder]

"Claudio Jolowicz" <cj***@doc.ic.ac.uk> wrote in message
news:Pi*******************************@kiwi.doc.ic .ac.uk...

On Wed, 21 Apr 2004, John Harrison wrote:

"bob holder" <holder25AThotmailDOTcom> wrote in message
news:Hw********@news.boeing.com...

Hi folks, I have a question. Can I use a named constructor with templates? If yes I am not sure the syntax. For example:

[snip]
I need to control the construction process, hence the need to hide the
default ctor.

thanks,
bob

Like this

#include <cstdlib>

template <size_t N> class ABC
{
public:
typedef ABC<N> *handle;
static handle create() { return new ABC<N>(); }

private: //I think you forgot this bit
ABC() {/*whatever*/}

};

int main ()
{
ABC<5>::handle my_abc;

my_abc = ABC<5>::create();
}

Bob, do you really want to use a template here? The obvious solution
would have been:

class ABC
{
public:
ABC(size_t);
};

This automatically hides the default constructor.

--
Claudio Jolowicz
http://www.doc.ic.ac.uk/~cj603

Thank you both John and Claudio. Just needed to get the syntax straight.

Claudio, you are correct that the default ctor needs to be declared as you
listed. I trimmed down the snippet a bit too much. I do want a template for
other reasons not obvious by such a small post.

Thanks to you both.
bob

[Siemel Naran]

"bob holder" <holder25AThotmailDOTcom> wrote in message
news:Hw********@news.boeing.com...

template <size_t N> class ABC {

public:
typedef ABC<N> *handle;

static handle create(size_t s) { return new ABC<s>(); }

private:
ABC();
};

This is not possible. Non-type template arguments must be integral
constants known at compile time, but you could read 's' from a file and then
call create(s).

You can have just

static handle create() { return new ABC<N>(); }

The other thing is that ABC<6> does not derive from ABC<5>, but your code
suggests casting an ABC<s> into an ABC<N> which is illegal.

But it's not clear what you're asking for.

[bob holder]

"Siemel Naran" <Si*********@REMOVE.att.net> wrote in message
news:Ij*******************@bgtnsc05-news.ops.worldnet.att.net...

"bob holder" <holder25AThotmailDOTcom> wrote in message
news:Hw********@news.boeing.com...

template <size_t N> class ABC {

public:
typedef ABC<N> *handle;

static handle create(size_t s) { return new ABC<s>(); }

private:
ABC();
};
This is not possible. Non-type template arguments must be integral
constants known at compile time, but you could read 's' from a file and

then call create(s).

You can have just

static handle create() { return new ABC<N>(); }

The other thing is that ABC<6> does not derive from ABC<5>, but your code
suggests casting an ABC<s> into an ABC<N> which is illegal.

But it's not clear what you're asking for.

Right you are Siemel. I understood the compile time constant issue, I just
stumbled over the syntax.

I do not require ABC<6> to derive from ABC<5>. ABC does not mean abstract
base class here. I should have chosen a better name, perhaps xyzzy.

Thanks,
bob