Mixing
How can I specialise a template with a template?
Consider a template class
template<class T>
class Foo
{
};
for which I can write a simple specialisation
template<>
class Foo<int>
{
};
I have a situation where I want to specialise Foo with a template class, in detail with a bool which serves as a compile-time flag:
template<>
class Foo<int, bool> // Clearly not the correct notation.
{
}
Uses would include Foo<1, true> and Foo<1, false>.
What is the correct notation for the class name, where I've marked "Clearly not the correct notation."?
I code to the C++11 standard.
c++ c++11 templates
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
add a comment |
Consider a template class
template<class T>
class Foo
{
};
for which I can write a simple specialisation
template<>
class Foo<int>
{
};
I have a situation where I want to specialise Foo with a template class, in detail with a bool which serves as a compile-time flag:
template<>
class Foo<int, bool> // Clearly not the correct notation.
{
}
Uses would include Foo<1, true> and Foo<1, false>.
What is the correct notation for the class name, where I've marked "Clearly not the correct notation."?
I code to the C++11 standard.
c++ c++11 templates
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
Foo<T>andFoo<T, E>are different templates.
– Dan M.
Nov 21 '18 at 16:11
It's not clear to me what you mean by "I want to specialise Foo with a template class" but you might want to specialize with a type that encodes both types, likeFoo<std::tuple<int, bool>>.
– François Andrieux
Nov 21 '18 at 16:11
add a comment |
Consider a template class
template<class T>
class Foo
{
};
for which I can write a simple specialisation
template<>
class Foo<int>
{
};
I have a situation where I want to specialise Foo with a template class, in detail with a bool which serves as a compile-time flag:
template<>
class Foo<int, bool> // Clearly not the correct notation.
{
}
Uses would include Foo<1, true> and Foo<1, false>.
What is the correct notation for the class name, where I've marked "Clearly not the correct notation."?
I code to the C++11 standard.
c++ c++11 templates
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
Consider a template class
template<class T>
class Foo
{
};
for which I can write a simple specialisation
template<>
class Foo<int>
{
};
I have a situation where I want to specialise Foo with a template class, in detail with a bool which serves as a compile-time flag:
template<>
class Foo<int, bool> // Clearly not the correct notation.
{
}
Uses would include Foo<1, true> and Foo<1, false>.
What is the correct notation for the class name, where I've marked "Clearly not the correct notation."?
I code to the C++11 standard.
c++ c++11 templates
c++ c++11 templates
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
asked Nov 21 '18 at 16:08
Sasidiran SangamanautramSasidiran Sangamanautram
20327
20327
Foo<T>andFoo<T, E>are different templates.
– Dan M.
Nov 21 '18 at 16:11
It's not clear to me what you mean by "I want to specialise Foo with a template class" but you might want to specialize with a type that encodes both types, likeFoo<std::tuple<int, bool>>.
– François Andrieux
Nov 21 '18 at 16:11
add a comment |
Foo<T>andFoo<T, E>are different templates.
– Dan M.
Nov 21 '18 at 16:11
It's not clear to me what you mean by "I want to specialise Foo with a template class" but you might want to specialize with a type that encodes both types, likeFoo<std::tuple<int, bool>>.
– François Andrieux
Nov 21 '18 at 16:11
Foo<T> and Foo<T, E> are different templates.– Dan M.
Nov 21 '18 at 16:11
Foo<T> and Foo<T, E> are different templates.– Dan M.
Nov 21 '18 at 16:11
It's not clear to me what you mean by "I want to specialise Foo with a template class" but you might want to specialize with a type that encodes both types, like
Foo<std::tuple<int, bool>>.– François Andrieux
Nov 21 '18 at 16:11
It's not clear to me what you mean by "I want to specialise Foo with a template class" but you might want to specialize with a type that encodes both types, like
Foo<std::tuple<int, bool>>.– François Andrieux
Nov 21 '18 at 16:11
add a comment |
3 Answers
3
active
oldest
votes
Seems like default value for template argument.
template<class T, bool flag = false>
class Foo
{
};
template<>
class Foo<int>
{
//"false" specialization (default)
};
template<>
class Foo<int, true>
{
//"true" specialization
};
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
add a comment |
You need to change the primary template to
template<class T, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<int, true>
{
};
template<>
class Foo<int, false>
{
};
...
and then you would use it like
Foo<int, true> FooT;
Foo<int, false> FooF;
If you are going to use values for the first parameter like
Foo<1, true>
Then the primary template should be
template<int I, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<1, true>
{
};
template<>
class Foo<1, false>
{
};
...
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
Thanks. I think I'll do it this way.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
@SasidiranSangamanautram I just noticed in your Q you want to useFoolikeFoo<1, true>. Is that really what you want to useFoo?
– NathanOliver
Nov 21 '18 at 16:20
Almost yes, the first argument is actually an enum but I simplified it to an int.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:33
@SasidiranSangamanautram Okay. I've added to the answer how to get that since what I first proposed is different.
– NathanOliver
Nov 21 '18 at 16:35
add a comment |
This is not directly possible. Your template wants a single parameter, you can't specialize it for two. However, you can (partially) specialize it for some other type which is a template of two parameters.
Example:
template<class T>
class Foo;
template<int, bool> class tag;
template<int>
class Foo<tag<int, true>> { ... };
template<int>
class Foo<tag<int, false>> { ... };
And than you can use it
Foo<tag<1, true>> foo;
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
That's good to know. Thank you.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
Seems like default value for template argument.
template<class T, bool flag = false>
class Foo
{
};
template<>
class Foo<int>
{
//"false" specialization (default)
};
template<>
class Foo<int, true>
{
//"true" specialization
};
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
add a comment |
Seems like default value for template argument.
template<class T, bool flag = false>
class Foo
{
};
template<>
class Foo<int>
{
//"false" specialization (default)
};
template<>
class Foo<int, true>
{
//"true" specialization
};
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
add a comment |
Seems like default value for template argument.
template<class T, bool flag = false>
class Foo
{
};
template<>
class Foo<int>
{
//"false" specialization (default)
};
template<>
class Foo<int, true>
{
//"true" specialization
};
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
Seems like default value for template argument.
template<class T, bool flag = false>
class Foo
{
};
template<>
class Foo<int>
{
//"false" specialization (default)
};
template<>
class Foo<int, true>
{
//"true" specialization
};
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
answered Nov 21 '18 at 16:41
YuriyYuriy
1679
1679
add a comment |
add a comment |
You need to change the primary template to
template<class T, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<int, true>
{
};
template<>
class Foo<int, false>
{
};
...
and then you would use it like
Foo<int, true> FooT;
Foo<int, false> FooF;
If you are going to use values for the first parameter like
Foo<1, true>
Then the primary template should be
template<int I, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<1, true>
{
};
template<>
class Foo<1, false>
{
};
...
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
Thanks. I think I'll do it this way.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
@SasidiranSangamanautram I just noticed in your Q you want to useFoolikeFoo<1, true>. Is that really what you want to useFoo?
– NathanOliver
Nov 21 '18 at 16:20
Almost yes, the first argument is actually an enum but I simplified it to an int.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:33
@SasidiranSangamanautram Okay. I've added to the answer how to get that since what I first proposed is different.
– NathanOliver
Nov 21 '18 at 16:35
add a comment |
You need to change the primary template to
template<class T, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<int, true>
{
};
template<>
class Foo<int, false>
{
};
...
and then you would use it like
Foo<int, true> FooT;
Foo<int, false> FooF;
If you are going to use values for the first parameter like
Foo<1, true>
Then the primary template should be
template<int I, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<1, true>
{
};
template<>
class Foo<1, false>
{
};
...
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
Thanks. I think I'll do it this way.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
@SasidiranSangamanautram I just noticed in your Q you want to useFoolikeFoo<1, true>. Is that really what you want to useFoo?
– NathanOliver
Nov 21 '18 at 16:20
Almost yes, the first argument is actually an enum but I simplified it to an int.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:33
@SasidiranSangamanautram Okay. I've added to the answer how to get that since what I first proposed is different.
– NathanOliver
Nov 21 '18 at 16:35
add a comment |
You need to change the primary template to
template<class T, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<int, true>
{
};
template<>
class Foo<int, false>
{
};
...
and then you would use it like
Foo<int, true> FooT;
Foo<int, false> FooF;
If you are going to use values for the first parameter like
Foo<1, true>
Then the primary template should be
template<int I, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<1, true>
{
};
template<>
class Foo<1, false>
{
};
...
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
You need to change the primary template to
template<class T, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<int, true>
{
};
template<>
class Foo<int, false>
{
};
...
and then you would use it like
Foo<int, true> FooT;
Foo<int, false> FooF;
If you are going to use values for the first parameter like
Foo<1, true>
Then the primary template should be
template<int I, bool B>
class Foo
{
};
and then you can specialize it like
template<>
class Foo<1, true>
{
};
template<>
class Foo<1, false>
{
};
...
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
edited Nov 21 '18 at 16:35
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
answered Nov 21 '18 at 16:12
NathanOliverNathanOliver
92.4k16129195
92.4k16129195
Thanks. I think I'll do it this way.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
@SasidiranSangamanautram I just noticed in your Q you want to useFoolikeFoo<1, true>. Is that really what you want to useFoo?
– NathanOliver
Nov 21 '18 at 16:20
Almost yes, the first argument is actually an enum but I simplified it to an int.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:33
@SasidiranSangamanautram Okay. I've added to the answer how to get that since what I first proposed is different.
– NathanOliver
Nov 21 '18 at 16:35
add a comment |
Thanks. I think I'll do it this way.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
@SasidiranSangamanautram I just noticed in your Q you want to useFoolikeFoo<1, true>. Is that really what you want to useFoo?
– NathanOliver
Nov 21 '18 at 16:20
Almost yes, the first argument is actually an enum but I simplified it to an int.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:33
@SasidiranSangamanautram Okay. I've added to the answer how to get that since what I first proposed is different.
– NathanOliver
Nov 21 '18 at 16:35
Thanks. I think I'll do it this way.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
Thanks. I think I'll do it this way.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
@SasidiranSangamanautram I just noticed in your Q you want to use
Foo like Foo<1, true>. Is that really what you want to use Foo?– NathanOliver
Nov 21 '18 at 16:20
@SasidiranSangamanautram I just noticed in your Q you want to use
Foo like Foo<1, true>. Is that really what you want to use Foo?– NathanOliver
Nov 21 '18 at 16:20
Almost yes, the first argument is actually an enum but I simplified it to an int.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:33
Almost yes, the first argument is actually an enum but I simplified it to an int.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:33
@SasidiranSangamanautram Okay. I've added to the answer how to get that since what I first proposed is different.
– NathanOliver
Nov 21 '18 at 16:35
@SasidiranSangamanautram Okay. I've added to the answer how to get that since what I first proposed is different.
– NathanOliver
Nov 21 '18 at 16:35
add a comment |
This is not directly possible. Your template wants a single parameter, you can't specialize it for two. However, you can (partially) specialize it for some other type which is a template of two parameters.
Example:
template<class T>
class Foo;
template<int, bool> class tag;
template<int>
class Foo<tag<int, true>> { ... };
template<int>
class Foo<tag<int, false>> { ... };
And than you can use it
Foo<tag<1, true>> foo;
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
That's good to know. Thank you.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
add a comment |
This is not directly possible. Your template wants a single parameter, you can't specialize it for two. However, you can (partially) specialize it for some other type which is a template of two parameters.
Example:
template<class T>
class Foo;
template<int, bool> class tag;
template<int>
class Foo<tag<int, true>> { ... };
template<int>
class Foo<tag<int, false>> { ... };
And than you can use it
Foo<tag<1, true>> foo;
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
That's good to know. Thank you.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
add a comment |
This is not directly possible. Your template wants a single parameter, you can't specialize it for two. However, you can (partially) specialize it for some other type which is a template of two parameters.
Example:
template<class T>
class Foo;
template<int, bool> class tag;
template<int>
class Foo<tag<int, true>> { ... };
template<int>
class Foo<tag<int, false>> { ... };
And than you can use it
Foo<tag<1, true>> foo;
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
This is not directly possible. Your template wants a single parameter, you can't specialize it for two. However, you can (partially) specialize it for some other type which is a template of two parameters.
Example:
template<class T>
class Foo;
template<int, bool> class tag;
template<int>
class Foo<tag<int, true>> { ... };
template<int>
class Foo<tag<int, false>> { ... };
And than you can use it
Foo<tag<1, true>> foo;
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
answered Nov 21 '18 at 16:12
SergeyASergeyA
43.1k53886
43.1k53886
That's good to know. Thank you.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
add a comment |
That's good to know. Thank you.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
That's good to know. Thank you.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
That's good to know. Thank you.
– Sasidiran Sangamanautram
Nov 21 '18 at 16:16
add a comment |
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Foo<T>andFoo<T, E>are different templates.– Dan M.
Nov 21 '18 at 16:11
It's not clear to me what you mean by "I want to specialise Foo with a template class" but you might want to specialize with a type that encodes both types, like
Foo<std::tuple<int, bool>>.– François Andrieux
Nov 21 '18 at 16:11