using a type alias when splitting template class into header and implementation file
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1
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I have a templated class which is split into a .hpp file and a .ipp which has quite a long type in it. While refactoring I wanted to write a type alias for that type so the code could be a lot more readable. But no matter what I do I cannot get the type alias to be recognized in the .ipp file.
Here is a simple example of what I am trying to do:
container.hpp:
template <class T>
class container {
public:
using TypeAlias = T;
container(const TypeAlias& a);
const TypeAlias& getA() const;
private:
TypeAlias a;
};
#include "container.ipp"
container.ipp:
template <class T>
container<T>::container(const TypeAlias& a) : a(a)
{
}
template <class T>
const TypeAlias& container<T>::getA() const
{
return this->a;
}
When compiling this the following error occurs:
./container.ipp:8:7: error: unknown type name 'TypeAlias'
const TypeAlias& container<T>::getA() const
Obviously in this case it doesn't make much sense to introduce the TypeAlias but in my actual program it could make a huge difference. Is there anything I can do to make the TypeAlias available in the .ipp file?
c++ templates typedef using
edited Nov 10 at 14:13
melpomene
58.1k54489
asked Nov 10 at 14:01
John Smith
411620
add a comment |
up vote
1
down vote
favorite
I have a templated class which is split into a .hpp file and a .ipp which has quite a long type in it. While refactoring I wanted to write a type alias for that type so the code could be a lot more readable. But no matter what I do I cannot get the type alias to be recognized in the .ipp file.
Here is a simple example of what I am trying to do:
container.hpp:
template <class T>
class container {
public:
using TypeAlias = T;
container(const TypeAlias& a);
const TypeAlias& getA() const;
private:
TypeAlias a;
};
#include "container.ipp"
container.ipp:
template <class T>
container<T>::container(const TypeAlias& a) : a(a)
{
}
template <class T>
const TypeAlias& container<T>::getA() const
{
return this->a;
}
When compiling this the following error occurs:
./container.ipp:8:7: error: unknown type name 'TypeAlias'
const TypeAlias& container<T>::getA() const
Obviously in this case it doesn't make much sense to introduce the TypeAlias but in my actual program it could make a huge difference. Is there anything I can do to make the TypeAlias available in the .ipp file?
c++ templates typedef using
edited Nov 10 at 14:13
melpomene
58.1k54489
asked Nov 10 at 14:01
John Smith
411620
2
I assume the#include "container.ipp"is actually at the end of container.hpp, not at the beginning of container.ipp.
– aschepler
Nov 10 at 14:10
@aschepler Yes I copied it wrong.
– John Smith
Nov 10 at 14:13
add a comment |
up vote
1
down vote
favorite
up vote
1
down vote
favorite
I have a templated class which is split into a .hpp file and a .ipp which has quite a long type in it. While refactoring I wanted to write a type alias for that type so the code could be a lot more readable. But no matter what I do I cannot get the type alias to be recognized in the .ipp file.
Here is a simple example of what I am trying to do:
container.hpp:
template <class T>
class container {
public:
using TypeAlias = T;
container(const TypeAlias& a);
const TypeAlias& getA() const;
private:
TypeAlias a;
};
#include "container.ipp"
container.ipp:
template <class T>
container<T>::container(const TypeAlias& a) : a(a)
{
}
template <class T>
const TypeAlias& container<T>::getA() const
{
return this->a;
}
When compiling this the following error occurs:
./container.ipp:8:7: error: unknown type name 'TypeAlias'
const TypeAlias& container<T>::getA() const
Obviously in this case it doesn't make much sense to introduce the TypeAlias but in my actual program it could make a huge difference. Is there anything I can do to make the TypeAlias available in the .ipp file?
c++ templates typedef using
edited Nov 10 at 14:13
melpomene
58.1k54489
asked Nov 10 at 14:01
John Smith
411620
I have a templated class which is split into a .hpp file and a .ipp which has quite a long type in it. While refactoring I wanted to write a type alias for that type so the code could be a lot more readable. But no matter what I do I cannot get the type alias to be recognized in the .ipp file.
Here is a simple example of what I am trying to do:
container.hpp:
template <class T>
class container {
public:
using TypeAlias = T;
container(const TypeAlias& a);
const TypeAlias& getA() const;
private:
TypeAlias a;
};
#include "container.ipp"
container.ipp:
template <class T>
container<T>::container(const TypeAlias& a) : a(a)
{
}
template <class T>
const TypeAlias& container<T>::getA() const
{
return this->a;
}
When compiling this the following error occurs:
./container.ipp:8:7: error: unknown type name 'TypeAlias'
const TypeAlias& container<T>::getA() const
Obviously in this case it doesn't make much sense to introduce the TypeAlias but in my actual program it could make a huge difference. Is there anything I can do to make the TypeAlias available in the .ipp file?
c++ templates typedef using
c++ templates typedef using
edited Nov 10 at 14:13
melpomene
58.1k54489
asked Nov 10 at 14:01
John Smith
411620
edited Nov 10 at 14:13
melpomene
58.1k54489
asked Nov 10 at 14:01
John Smith
411620
edited Nov 10 at 14:13
melpomene
58.1k54489
edited Nov 10 at 14:13
melpomene
58.1k54489
edited Nov 10 at 14:13
melpomene
58.1k54489
58.1k54489
asked Nov 10 at 14:01
John Smith
411620
asked Nov 10 at 14:01
John Smith
411620
asked Nov 10 at 14:01
John Smith
411620
411620
2
I assume the#include "container.ipp"is actually at the end of container.hpp, not at the beginning of container.ipp.
– aschepler
Nov 10 at 14:10
@aschepler Yes I copied it wrong.
– John Smith
Nov 10 at 14:13
add a comment |
2
I assume the#include "container.ipp"is actually at the end of container.hpp, not at the beginning of container.ipp.
– aschepler
Nov 10 at 14:10
@aschepler Yes I copied it wrong.
– John Smith
Nov 10 at 14:13
2
2
I assume the
#include "container.ipp" is actually at the end of container.hpp, not at the beginning of container.ipp.– aschepler
Nov 10 at 14:10
I assume the
#include "container.ipp" is actually at the end of container.hpp, not at the beginning of container.ipp.– aschepler
Nov 10 at 14:10
@aschepler Yes I copied it wrong.
– John Smith
Nov 10 at 14:13
@aschepler Yes I copied it wrong.
– John Smith
Nov 10 at 14:13
add a comment |
1 Answer
1
active
oldest
votes
up vote
2
down vote
accepted
When you define a class member like container<T>::getA, things after the name of the member (getA here) are looked up in the scope of the class, but things before it are not. Essentially, if the compiler tries to understand things in order, when the declaration begins with const TypeAlias&, it doesn't yet know that it should look inside container<T> to figure out what TypeAlias could mean.
So using normal function syntax, you would need to specify that TypeAlias is a member type:
template <class T>
const typename container<T>::TypeAlias& container<T>::getA() const
{
return this->a;
}
But this is one advantage of the "trailing return type" syntax (valid in C++11 and later): Just by changing the order of things, it lets you use members of the class within the return type more simply:
template <class T>
auto container<T>::getA() const -> const TypeAlias&
{
return this->a;
}
answered Nov 10 at 14:09
aschepler
51.4k574126
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
When you define a class member like container<T>::getA, things after the name of the member (getA here) are looked up in the scope of the class, but things before it are not. Essentially, if the compiler tries to understand things in order, when the declaration begins with const TypeAlias&, it doesn't yet know that it should look inside container<T> to figure out what TypeAlias could mean.
So using normal function syntax, you would need to specify that TypeAlias is a member type:
template <class T>
const typename container<T>::TypeAlias& container<T>::getA() const
{
return this->a;
}
But this is one advantage of the "trailing return type" syntax (valid in C++11 and later): Just by changing the order of things, it lets you use members of the class within the return type more simply:
template <class T>
auto container<T>::getA() const -> const TypeAlias&
{
return this->a;
}
answered Nov 10 at 14:09
aschepler
51.4k574126
add a comment |
up vote
2
down vote
accepted
When you define a class member like container<T>::getA, things after the name of the member (getA here) are looked up in the scope of the class, but things before it are not. Essentially, if the compiler tries to understand things in order, when the declaration begins with const TypeAlias&, it doesn't yet know that it should look inside container<T> to figure out what TypeAlias could mean.
So using normal function syntax, you would need to specify that TypeAlias is a member type:
template <class T>
const typename container<T>::TypeAlias& container<T>::getA() const
{
return this->a;
}
But this is one advantage of the "trailing return type" syntax (valid in C++11 and later): Just by changing the order of things, it lets you use members of the class within the return type more simply:
template <class T>
auto container<T>::getA() const -> const TypeAlias&
{
return this->a;
}
answered Nov 10 at 14:09
aschepler
51.4k574126
add a comment |
up vote
2
down vote
accepted
up vote
2
down vote
accepted
When you define a class member like container<T>::getA, things after the name of the member (getA here) are looked up in the scope of the class, but things before it are not. Essentially, if the compiler tries to understand things in order, when the declaration begins with const TypeAlias&, it doesn't yet know that it should look inside container<T> to figure out what TypeAlias could mean.
So using normal function syntax, you would need to specify that TypeAlias is a member type:
template <class T>
const typename container<T>::TypeAlias& container<T>::getA() const
{
return this->a;
}
But this is one advantage of the "trailing return type" syntax (valid in C++11 and later): Just by changing the order of things, it lets you use members of the class within the return type more simply:
template <class T>
auto container<T>::getA() const -> const TypeAlias&
{
return this->a;
}
answered Nov 10 at 14:09
aschepler
51.4k574126
When you define a class member like container<T>::getA, things after the name of the member (getA here) are looked up in the scope of the class, but things before it are not. Essentially, if the compiler tries to understand things in order, when the declaration begins with const TypeAlias&, it doesn't yet know that it should look inside container<T> to figure out what TypeAlias could mean.
So using normal function syntax, you would need to specify that TypeAlias is a member type:
template <class T>
const typename container<T>::TypeAlias& container<T>::getA() const
{
return this->a;
}
But this is one advantage of the "trailing return type" syntax (valid in C++11 and later): Just by changing the order of things, it lets you use members of the class within the return type more simply:
template <class T>
auto container<T>::getA() const -> const TypeAlias&
{
return this->a;
}
answered Nov 10 at 14:09
aschepler
51.4k574126
answered Nov 10 at 14:09
aschepler
51.4k574126
answered Nov 10 at 14:09
aschepler
51.4k574126
answered Nov 10 at 14:09
aschepler
51.4k574126
51.4k574126
add a comment |
add a comment |
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2
I assume the
#include "container.ipp"is actually at the end of container.hpp, not at the beginning of container.ipp.– aschepler
Nov 10 at 14:10
@aschepler Yes I copied it wrong.
– John Smith
Nov 10 at 14:13