How to call a copy constructor only if it exist ? c++
2
I'm making an Entity-Component-System Engine and I have a little trouble with prefabs. I want to copy a prefab, only if the class that the user pass has template is copy constructible. A simple implementation of what I want to do will be something like that :
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if (std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if (std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
template<typename ...Args>
void addComponent(Args &&...args) {
store.emplace_back(std::make_shared<T>(args ...));
}
Is there a way to make this code working? Actually, it throws me that it can't create a specific class because it's a copy-constructible constructor is deleted (Which is the case).
Thanks in advance, and sorry for my mistakes I'm french ;)
c++ templates constructor variadic-functions copy-constructor
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
add a comment |
2
I'm making an Entity-Component-System Engine and I have a little trouble with prefabs. I want to copy a prefab, only if the class that the user pass has template is copy constructible. A simple implementation of what I want to do will be something like that :
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if (std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if (std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
template<typename ...Args>
void addComponent(Args &&...args) {
store.emplace_back(std::make_shared<T>(args ...));
}
Is there a way to make this code working? Actually, it throws me that it can't create a specific class because it's a copy-constructible constructor is deleted (Which is the case).
Thanks in advance, and sorry for my mistakes I'm french ;)
c++ templates constructor variadic-functions copy-constructor
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
Can you use C++17?
– NathanOliver
Nov 20 '18 at 22:50
Yes, I already compile with this version.
– LordFinn
Nov 20 '18 at 22:54
add a comment |
2
2
2
I'm making an Entity-Component-System Engine and I have a little trouble with prefabs. I want to copy a prefab, only if the class that the user pass has template is copy constructible. A simple implementation of what I want to do will be something like that :
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if (std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if (std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
template<typename ...Args>
void addComponent(Args &&...args) {
store.emplace_back(std::make_shared<T>(args ...));
}
Is there a way to make this code working? Actually, it throws me that it can't create a specific class because it's a copy-constructible constructor is deleted (Which is the case).
Thanks in advance, and sorry for my mistakes I'm french ;)
c++ templates constructor variadic-functions copy-constructor
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
I'm making an Entity-Component-System Engine and I have a little trouble with prefabs. I want to copy a prefab, only if the class that the user pass has template is copy constructible. A simple implementation of what I want to do will be something like that :
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if (std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if (std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
template<typename ...Args>
void addComponent(Args &&...args) {
store.emplace_back(std::make_shared<T>(args ...));
}
Is there a way to make this code working? Actually, it throws me that it can't create a specific class because it's a copy-constructible constructor is deleted (Which is the case).
Thanks in advance, and sorry for my mistakes I'm french ;)
c++ templates constructor variadic-functions copy-constructor
c++ templates constructor variadic-functions copy-constructor
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
edited Nov 20 '18 at 22:51
LordFinn
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
asked Nov 20 '18 at 22:48
LordFinnLordFinn
133
133
Can you use C++17?
– NathanOliver
Nov 20 '18 at 22:50
Yes, I already compile with this version.
– LordFinn
Nov 20 '18 at 22:54
add a comment |
Can you use C++17?
– NathanOliver
Nov 20 '18 at 22:50
Yes, I already compile with this version.
– LordFinn
Nov 20 '18 at 22:54
Can you use C++17?
– NathanOliver
Nov 20 '18 at 22:50
Can you use C++17?
– NathanOliver
Nov 20 '18 at 22:50
Yes, I already compile with this version.
– LordFinn
Nov 20 '18 at 22:54
Yes, I already compile with this version.
– LordFinn
Nov 20 '18 at 22:54
add a comment |
1 Answer
1
active
oldest
votes
3
If you have C++17, use if constexpr:
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if constexpr(std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if constexpr(std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
If you don't, you have to use SFINAE:
std::enable_if<std::is_copy_constructible<T>::value> addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
}
std::enable_if<!std::is_copy_constructible<T>::value && std::is_default_constructible<T>::value> addFromPrefab() {
addComponent(); // Add a new component with his default constructor
}
std::enable_if<!std::is_copy_constructible<T>::value && !std::is_default_constructible<T>::value> addFromPrefab() {
throw std::exception();
}
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
Thank you a lot, constexpr work perfectly!
– LordFinn
Nov 20 '18 at 22:59
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
3
If you have C++17, use if constexpr:
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if constexpr(std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if constexpr(std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
If you don't, you have to use SFINAE:
std::enable_if<std::is_copy_constructible<T>::value> addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
}
std::enable_if<!std::is_copy_constructible<T>::value && std::is_default_constructible<T>::value> addFromPrefab() {
addComponent(); // Add a new component with his default constructor
}
std::enable_if<!std::is_copy_constructible<T>::value && !std::is_default_constructible<T>::value> addFromPrefab() {
throw std::exception();
}
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
Thank you a lot, constexpr work perfectly!
– LordFinn
Nov 20 '18 at 22:59
add a comment |
3
If you have C++17, use if constexpr:
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if constexpr(std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if constexpr(std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
If you don't, you have to use SFINAE:
std::enable_if<std::is_copy_constructible<T>::value> addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
}
std::enable_if<!std::is_copy_constructible<T>::value && std::is_default_constructible<T>::value> addFromPrefab() {
addComponent(); // Add a new component with his default constructor
}
std::enable_if<!std::is_copy_constructible<T>::value && !std::is_default_constructible<T>::value> addFromPrefab() {
throw std::exception();
}
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
Thank you a lot, constexpr work perfectly!
– LordFinn
Nov 20 '18 at 22:59
add a comment |
3
3
3
If you have C++17, use if constexpr:
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if constexpr(std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if constexpr(std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
If you don't, you have to use SFINAE:
std::enable_if<std::is_copy_constructible<T>::value> addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
}
std::enable_if<!std::is_copy_constructible<T>::value && std::is_default_constructible<T>::value> addFromPrefab() {
addComponent(); // Add a new component with his default constructor
}
std::enable_if<!std::is_copy_constructible<T>::value && !std::is_default_constructible<T>::value> addFromPrefab() {
throw std::exception();
}
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
If you have C++17, use if constexpr:
void addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
if constexpr(std::is_copy_constructible<T>::value)
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
else if constexpr(std::is_default_constructible<T>::value)
addComponent(); // Add a new component with his default constructor
else
throw std::exception();
}
If you don't, you have to use SFINAE:
std::enable_if<std::is_copy_constructible<T>::value> addFromPrefab() { //We assume that _prefab is of type std::shared_ptr<T>
addComponent(*_prefab); // Add a new component by copy constructing the prefab passed as parameter
}
std::enable_if<!std::is_copy_constructible<T>::value && std::is_default_constructible<T>::value> addFromPrefab() {
addComponent(); // Add a new component with his default constructor
}
std::enable_if<!std::is_copy_constructible<T>::value && !std::is_default_constructible<T>::value> addFromPrefab() {
throw std::exception();
}
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
answered Nov 20 '18 at 22:52
Matthieu BrucherMatthieu Brucher
16.4k32143
16.4k32143
Thank you a lot, constexpr work perfectly!
– LordFinn
Nov 20 '18 at 22:59
add a comment |
Thank you a lot, constexpr work perfectly!
– LordFinn
Nov 20 '18 at 22:59
Thank you a lot, constexpr work perfectly!
– LordFinn
Nov 20 '18 at 22:59
Thank you a lot, constexpr work perfectly!
– LordFinn
Nov 20 '18 at 22:59
add a comment |
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Can you use C++17?
– NathanOliver
Nov 20 '18 at 22:50
Yes, I already compile with this version.
– LordFinn
Nov 20 '18 at 22:54