The following code works:
#include <iostream>
template<class T>
struct Test
{
T t;
template<class T, template<class U =3D T> class V>
Test<T>& foo(V<T>& f)
{
f.t =3D 5;
return *this;
}
};
int main() {
Test<int> t;
t.foo(t);
std::cout << t.t;
}
However, if I try to move the definition of the foo()-function outside
of the declaration like so:
template<typename T, template<typename U =3D T> class V>
Test<T>& Test<T>::foo(V<T>& f)
{
f.t =3D 5;
return *this;
}
It does not compile (VC++8.0) with the following error-message:
test.cpp(24) : error C2244: 'Test<T>::foo' : unable to match function
definition to an existing declaration
definition
'Test<T> &Test<T>::foo(V<T> &)'
existing declarations
'Test<T> &Test<T>::foo(V<T> &)'
Anyone have an idea of how to make this work?
--
Erik Wikstr=F6m
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 eriwik (500)
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12/14/2006 11:56:34 AM |
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Erik Wikstr�m wrote:
> The following code works:
>
> #include <iostream>
>
> template<class T>
> struct Test
> {
> T t;
> template<class T, template<class U = T> class V>
> Test<T>& foo(V<T>& f)
> {
> f.t = 5;
> return *this;
> }
> };
>
> int main() {
> Test<int> t;
> t.foo(t);
> std::cout << t.t;
>
> }
>
> However, if I try to move the definition of the foo()-function outside
> of the declaration like so:
>
> template<typename T, template<typename U = T> class V>
> Test<T>& Test<T>::foo(V<T>& f)
> {
> f.t = 5;
> return *this;
> }
>
> It does not compile (VC++8.0) with the following error-message:
>
> test.cpp(24) : error C2244: 'Test<T>::foo' : unable to match function
> definition to an existing declaration
> definition
> 'Test<T> &Test<T>::foo(V<T> &)'
> existing declarations
> 'Test<T> &Test<T>::foo(V<T> &)'
>
> Anyone have an idea of how to make this work?
The default argument in the function _definition_ looks wrong to me.
--
NOUN:1. Money or property bequeathed to another by will. 2. Something handed
down from an ancestor or a predecessor or from the past: a legacy of
religious freedom. ETYMOLOGY: MidE legacie, office of a deputy, from OF,
from ML legatia, from L legare, to depute, bequeath. www.bartleby.com/61/
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 chattengau (616)
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12/14/2006 12:03:36 PM
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On Dec 14, 1:03 pm, "Steven T. Hatton" <chatten...@germania.sup> wrote:
> Erik Wikstr=F6m wrote:
> > The following code works:
>
> > #include <iostream>
>
> > template<class T>
> > struct Test
> > {
> > T t;
> > template<class T, template<class U =3D T> class V>
> > Test<T>& foo(V<T>& f)
> > {
> > f.t =3D 5;
> > return *this;
> > }
> > };
>
> > int main() {
> > Test<int> t;
> > t.foo(t);
> > std::cout << t.t;
>
> > }
>
> > However, if I try to move the definition of the foo()-function outside
> > of the declaration like so:
>
> > template<typename T, template<typename U =3D T> class V>
> > Test<T>& Test<T>::foo(V<T>& f)
> > {
> > f.t =3D 5;
> > return *this;
> > }
>
> > It does not compile (VC++8.0) with the following error-message:
>
> > test.cpp(24) : error C2244: 'Test<T>::foo' : unable to match function
> > definition to an existing declaration
> > definition
> > 'Test<T> &Test<T>::foo(V<T> &)'
> > existing declarations
> > 'Test<T> &Test<T>::foo(V<T> &)'
>
> > Anyone have an idea of how to make this work?
>
>The default argument in the function _definition_ looks wrong to me.
You mean the U =3D T part? I tried with "template<class T,
template<class> class V>" instead but with no luck.
--
Erik Wikstr=F6m
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eriwik (500)
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12/14/2006 12:19:51 PM
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Erik Wikstr�m wrote:
> #include <iostream>
>
> template<class T>
> struct Test
> {
> T t;
> template<class T, template<class U = T> class V>
> Test<T>& foo(V<T>& f)
> {
> f.t = 5;
> return *this;
> }
> };
>
> int main() {
> Test<int> t;
> t.foo(t);
> std::cout << t.t;
>
> }
>
> However, if I try to move the definition of the foo()-function outside
> of the declaration like so:
>
> template<typename T, template<typename U = T> class V>
> Test<T>& Test<T>::foo(V<T>& f)
> {
> f.t = 5;
> return *this;
> }
The first form doesn't compile for me with GCC 4.0.2. Have I got it right?
//templ.cpp
#include <iostream>
template<class T>
struct Test
{
T t;
template<class T, template<class U = T> class V>
Test<T>& foo(V<T>& f)
{
f.t = 5;
return *this;
}
};
int main() {
Test<int> t;
t.foo(t);
std::cout << t.t;
}
//---------------EOF-----------------
g++ -o templ templ.cpp
templ.cpp:7: error: declaration of ?class T?
templ.cpp:3: error: shadows template parm ?class T?
Compilation exited abnormally with code 1 at Thu Dec 14 07:47:26
--
NOUN:1. Money or property bequeathed to another by will. 2. Something handed
down from an ancestor or a predecessor or from the past: a legacy of
religious freedom. ETYMOLOGY: MidE legacie, office of a deputy, from OF,
from ML legatia, from L legare, to depute, bequeath. www.bartleby.com/61/
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chattengau (616)
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12/14/2006 12:52:10 PM
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Erik Wikstr=F6m wrote:
> The following code works:
>
> #include <iostream>
>
> template<class T>
> struct Test
> {
> T t;
> template<class T, template<class U =3D T> class V>
> Test<T>& foo(V<T>& f)
> {
> f.t =3D 5;
> return *this;
> }
> };
>
> int main() {
> Test<int> t;
> t.foo(t);
> std::cout << t.t;
>
> }
The program is using "T" as the name of two separate type parameters,
So I would suggest giving each parameter a distinct name, maybe T1 and
T2, so that the compiler can tell them part.
Greg
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 greghe (676)
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12/14/2006 1:00:46 PM
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On Dec 14, 1:52 pm, "Steven T. Hatton" <chatten...@germania.sup> wrote:
>
>The first form doesn't compile for me with GCC 4.0.2. Have I got it right?
>
> //templ.cpp
> #include <iostream>
>
> template<class T>
> struct Test
> {
> T t;
> template<class T, template<class U =3D T> class V>
> Test<T>& foo(V<T>& f)
> {
> f.t =3D 5;
> return *this;
> }
>
> };int main() {
> Test<int> t;
> t.foo(t);
> std::cout << t.t;}//---------------EOF-----------------
>
> g++ -o templ templ.cpp
> templ.cpp:7: error: declaration of ?class T?
> templ.cpp:3: error: shadows template parm ?class T?
Yes, that looks right, however I finally managed to find a working
solution:
#include <iostream>
template<class T>
struct Test
{
T t;
template<template<class U =3D T> class V>
Test<T>& foo(V<T>& f);
};
template<class T>
template<template<class> class V>
Test<T>& Test<T>::foo(V<T>& f)
{
f.t =3D 5;
return *this;
}
int main() {
Test<int> t;
t.foo(t);
std::cout << t.t;
}
Once again, the "template<template<class U =3D T> class V>" can be
reduced to "template<template<class> class V>" but I think that it
documents the intention that the type that V is parametrized by is the
same as that of Test.
--
Erik Wikstr=F6m
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eriwik (500)
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12/14/2006 1:04:38 PM
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5 Replies
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