Function templates

[al]

1. If a function template is defined:

template <typename A>
A SQ(A& a)
{
return a*a;
}

How could prevent users from passing a type which makes no sense, like
Employee class type?

2. If Employee is pass as T in the template below, should an assignment
operator have to be defined since there're assignment operation in the
function?

template <class T>
void swap(T& x, T& y)
{
T temp;
temp = x;
x = y;
y = temp;
}

3. Is "template <class T>" equivalent to "template <typename T>"?

Thanks!

[Ron Natalie]

"al" <al***@168.ne t> wrote in message news:ne******** *************** @bgtnsc04-news.ops.worldn et.att.net...

1. If a function template is defined:

How could prevent users from passing a type which makes no sense, like
Employee class type?
You can't, anymore than you can stop them from writing
Employee() * Employee()
other than the compiler bitching about * not being defined for those
types.

2. If Employee is pass as T in the template below, should an assignment
operator have to be defined since there're assignment operation in the
function?
There has to be one accessible. Of course, operator= will be defined
in a class if the user doesn't declare one.
3. Is "template <class T>" equivalent to "template <typename T>"?

Yes. <class T> will match any type, not just class types. Typename
and class are interchangeable in this context.

[Cy Edmunds]

"al" <al***@168.ne t> wrote in message
news:ne******** *************** @bgtnsc04-news.ops.worldn et.att.net...

1. If a function template is defined:

template <typename A>
A SQ(A& a)
{
return a*a;
}

How could prevent users from passing a type which makes no sense, like
Employee class type?
Let 'em try. It won't compile. Of course the error message may be a bit
obscure.

2. If Employee is pass as T in the template below, should an assignment
operator have to be defined since there're assignment operation in the
function?

template <class T>
void swap(T& x, T& y)
{
T temp;
temp = x;
x = y;
y = temp;
}
If you don't write an assignment operator the compiler will provide you with
one which just copies the bits.

3. Is "template <class T>" equivalent to "template <typename T>"?
Yes. The keyword "typename" was a relatively late addition to the language.
It makes more sense in this context then "class".

Thanks!

--
Cy
http://home.rochester.rr.com/cyhome/

[Gianni Mariani]

al wrote:

1. If a function template is defined:

template <typename A>
A SQ(A& a)
{
return a*a;
}

How could prevent users from passing a type which makes no sense, like
Employee class type?

You can create a specialization like:

template <typename A>
A SQ(A& a)
{
return a*a;
}

template <>
Employee SQ(Employee& a)
{
... some code that compiles to an error ...
}

However if you don't provide a 'operator *()', your original SQ provides
for an error anyway.

[Ron Natalie]

"Cy Edmunds" <ce******@spaml ess.rochester.r r.com> wrote in message news:Wx******** ***********@twi ster.nyroc.rr.c om...

If you don't write an assignment operator the compiler will provide you with
one which just copies the bits.

Well, more specifically, it invokes the assignment semantics of all the subobjects
(bases and non-static members).

[Cy Edmunds]

"Ron Natalie" <ro*@sensor.com > wrote in message
news:3f******** *************** @news.newshosti ng.com...

"Cy Edmunds" <ce******@spaml ess.rochester.r r.com> wrote in message news:Wx******** ***********@twi ster.nyroc.rr.c om...

If you don't write an assignment operator the compiler will provide you with

one which just copies the bits.
Well, more specifically, it invokes the assignment semantics of all the

subobjects (bases and non-static members).

Right! When I first started C++ I worried about that.

--
Cy
http://home.rochester.rr.com/cyhome/

[Rolf Magnus]

Chris Mantoulidis wrote:

"Cy Edmunds" <ce******@spaml ess.rochester.r r.com> wrote in message
news:<Wx******* ************@tw ister.nyroc.rr. com>...

"al" <al***@168.ne t> wrote in message
news:ne******** *************** @bgtnsc04-news.ops.worldn et.att.net...

> 1. If a function template is defined:
>
> template <typename A>
> A SQ(A& a)
> {
> return a*a;
> }
>
> How could prevent users from passing a type which makes no sense,
> like Employee class type?
Let 'em try. It won't compile. Of course the error message may be a
bit obscure.

>
> 2. If Employee is pass as T in the template below, should an
> assignment operator have to be defined since there're assignment
> operation in the function?
>
> template <class T>
> void swap(T& x, T& y)
> {
> T temp;
> temp = x;
> x = y;
> y = temp;
> }

If you don't write an assignment operator the compiler will provide
you with one which just copies the bits.

>
> 3. Is "template <class T>" equivalent to "template <typename T>"?

Yes. The keyword "typename" was a relatively late addition to the
language. It makes more sense in this context then "class".

So, <class T> allows ANY KINDA class and type (int, char, etc.) to be
passed as the template whereas <template T> allows just types??

What do you mean by "just types"? classes _are_ types.
Is that it? Cuz I'm a bit confused.

Again, there is no difference between <class T> and <typename T> (not
<template T> btw - I guess that was a typo).

[Chris Mantoulidis]

Jacques Labuschagne <ja*****@clawsh rimp.com> wrote in message news:<vo******* *************@n ews02.tsnz.net> ...

Chris Mantoulidis wrote:

So, <class T> allows ANY KINDA class and type (int, char, etc.) to be
passed as the template whereas <template T> allows just types?? Is
that it? Cuz I'm a bit confused.
No, the two are equivalent. You can't restrict T, but you can use T in
such a way that it only compiles with compatible types.

compatible types = int, char, etc. ???
Then what's the difference between typename and class... You don't really explain

Thanks,
cmad

template<typena me T>
void foo(const T& some_object){
some_object.unu sual_function() ;
}

or even

template<typena me T>
T bar(const T& some_object){
T other_object; // requires T default constructable.
other_object = some_object; // requires T copyable.
return some_object + other_object; // requires operator+
}

[Jacques Labuschagne]

Chris Mantoulidis wrote:

Jacques Labuschagne <ja*****@clawsh rimp.com> wrote in message news:<vo******* *************@n ews02.tsnz.net> ...

Chris Mantoulidis wrote:

So, <class T> allows ANY KINDA class and type (int, char, etc.) to be
passed as the template whereas <template T> allows just types?? Is
that it? Cuz I'm a bit confused.
No, the two are equivalent. You can't restrict T, but you can use T in
such a way that it only compiles with compatible types.

compatible types = int, char, etc. ???

Compatible types == ones supporting the required operations (assignment,
default construction, etc). There's no difference between fundamental
types (int, char, etc) and user-defined types from a template's point of
view.


Then what's the difference between typename and class... You don't really explain

I said the two are equivalent. There is no difference.

Jacques.

[Howard Hinnant]

In article <vo************ ********@news02 .tsnz.net>,
Jacques Labuschagne <ja*****@clawsh rimp.com> wrote:

You can't restrict T, but you can use T in
such a way that it only compiles with compatible types.

You can also restrict T for the purpose of guiding overload resolution
(though it is far from clear that that is what the OP needed). Search
for "restrict_t o" and "enable_if" .

-Howard