points of instantiation

[anon]

Hello,

I am reading the "c++ templates - the complete guide" book, and I found
something very strange.

On the pages 146-147, there is the example about the points of
instantiations. I wasn't lazy, and I made the full example like this:


///// code
#include <iostream>
using namespace std;

class MyInt
{
public:
MyInt(int i):i(i)
{
cout<<"MyInt() i="<<i<<endl;
}
~MyInt()
{
cout<<"~MyInt() i="<<i<<endl;
}
int i;
};
MyInt operator-(const MyInt& a )
{
return MyInt(a.i-1);
}
bool operator >(const MyInt &a,const MyInt &b)
{
return a.i>b.i;
}

typedef MyInt Int;

template < typename T >
void f(T i )
{
if ( i>T(0) )
{
g(-i);
}
}

void g(Int i)
{
f<Int>(i);
}
int main()
{
Int a(5);
g(a);
}

///// code

The book says that if I replace:
typedef MyInt Int;
with
typedef int Int;
the example will no longer compile, which is not true.

Can anyone (who has access to the book) explain why they wrote it should
not compile?

I am using g++ 4.1.3

[Fraser Ross]

Re: points of instantiation

A footnote mentions that the code is using a part of the language that
is under review. Does your copy not have that? The program doesn't
compile with int because ADL isn't done for the built in types.

Fraser.

[anon]

Re: points of instantiation

Fraser Ross wrote:

A footnote mentions that the code is using a part of the language that
is under review. Does your copy not have that? The program doesn't
compile with int because ADL isn't done for the built in types.

My book has the footnote, but the problem is my example is compiling
when I replace MyInt with int.

Can you suggest a modification to my example that demonstrates what they
wanted to show?

[diamondback]

Re: points of instantiation

On Sep 22, 3:26 am, anon <a...@no.invali dwrote:

Hello,
>
I am reading the "c++ templates - the complete guide" book, and I found
something very strange.
>
On the pages 146-147, there is the example about the points of
instantiations. I wasn't lazy, and I made the full example like this:
>
///// code
#include <iostream>
using namespace std;
>
class MyInt
{
     public:
         MyInt(int i):i(i)
         {
             cout<<"MyInt() i="<<i<<endl;
         }
         ~MyInt()
         {
             cout<<"~MyInt() i="<<i<<endl;
         }
         int i;};
>
MyInt operator-(const MyInt& a )
{
     return MyInt(a.i-1);}
>
bool operator >(const MyInt &a,const MyInt &b)
{
     return a.i>b.i;
>
}
>
typedef MyInt Int;
>
template < typename T >
void f(T i )
{
     if ( i>T(0) )
     {
         g(-i);
     }
>
}
>
void g(Int i)
{
     f<Int>(i);}
>
int main()
{
     Int a(5);
     g(a);
>
}
>
///// code
>
The book says that if I replace:
typedef MyInt Int;
with
typedef int Int;
the example will no longer compile, which is not true.
>
Can anyone (who has access to the book) explain why they wrote it should
not compile?
>
I am using g++ 4.1.3

This sounds like an error in the text to me. It is wrong for a
programming text to state, unequivocally that something will/will not
compile. The intent is obviously *should* not compile. But, there is
always an exception based on standards, compiler, hardware, version,
etc. In this case, it seems that your g++ is fine with the construct
for some reason. Different compilers may have various different
responses.

[Triple-DES]

Re: points of instantiation

On 22 Sep, 20:31, diamondback <christopher... .@gmail.comwrot e:

On Sep 22, 3:26 am, anon <a...@no.invali dwrote:

[example from C++ Templates p146-147]

The book says that if I replace:
typedef MyInt Int;
with
typedef int Int;
the example will no longer compile, which is not true.

>

Can anyone (who has access to the book) explain why they wrote it should
not compile?

>

I am using g++ 4.1.3

>
This sounds like an error in the text to me. It is wrong for a
programming text to state, unequivocally that something will/will not
compile. The intent is obviously *should* not compile.

Actually, the exact wording is: "(...) the previous example _should_
no longer compile".

But, there is
always an exception based on standards, compiler, hardware, version,
etc. In this case, it seems that your g++ is fine with the construct
for some reason. Different compilers may have various different
responses.

True, but successfully compiling the example program (an ill-formed
program) without issuing a diagnostic is prohibited by the C++
standard.

DP

[anon]

Re: points of instantiation

Triple-DES wrote:

On 22 Sep, 20:31, diamondback <christopher... .@gmail.comwrot e:

>On Sep 22, 3:26 am, anon <a...@no.invali dwrote:

>
[example from C++ Templates p146-147]
>

>>The book says that if I replace:
>>typedef MyInt Int;
>>with
>>typedef int Int;
>>the example will no longer compile, which is not true.
>>Can anyone (who has access to the book) explain why they wrote it should
>>not compile?
>>I am using g++ 4.1.3

>This sounds like an error in the text to me. It is wrong for a
>programming text to state, unequivocally that something will/will not
>compile. The intent is obviously *should* not compile.

>
Actually, the exact wording is: "(...) the previous example _should_
no longer compile".
>

>But, there is
>always an exception based on standards, compiler, hardware, version,
>etc. In this case, it seems that your g++ is fine with the construct
>for some reason. Different compilers may have various different
>responses.

>
True, but successfully compiling the example program (an ill-formed
program) without issuing a diagnostic is prohibited by the C++
standard.

I tried (as Michael Doubez suggested) to use comeau online to compile
the example, and it failed.

I was surprised when the g++ accepted that without even the warning
(with -pedantic -ansi -Wall)