In C++11/14, an object can be transfered by move
or smark pointer.
(1) This is an example for move
:
class MoveClass {
private:
int *tab_;
int alloc_;
void Reset() {
tab_ = nullptr;
alloc_ = 0;
}
void Release() {
if (tab_) delete[] tab_;
tab_ = nullptr;
alloc_ = 0;
}
public:
MoveClass() : tab_(nullptr), alloc_(0) {}
~MoveClass() {
Release();
}
MoveClass(MoveClass && other) : tab_( other.tab_ ), alloc_( other.alloc_ ) {
other.Reset();
}
MoveClass & operator=(MoveClass && other) {
if (this == &other) return *this;
std::swap(tab_, other.tab_);
std::swap(alloc_, other.alloc_);
return *this;
}
void DoSomething() { /*...*/ }
};
When we use this movable MoveClass
, we can write code like this :
int main() {
MoveClass a;
a.DoSomething(); // now a has some memory resource
MoveClass b = std::move(a); // move a to b
return 0;
}
Always write move-constructor/move-operator= is boring, use shared_ptr/unique_ptr some times have the same effect, just like java, reference/pointer everywhere.
(2) Here is the example:
class NoMoveClass {
private:
int *tab_;
int alloc_;
void Release() {
if (tab_) delete[] tab_;
tab_ = nullptr;
alloc_ = 0;
}
public:
NoMoveClass() : tab_(nullptr), alloc_(0) {}
~NoMoveClass() {
Release();
}
MoveClass(MoveClass && other) = delete;
MoveClass & operator=(MoveClass && other) = delete;
void DoSomething() { /*...*/ }
};
We can use it like this:
int main() {
std::shared_ptr<NoMoveClass> a(new NoMoveClass());
a->DoSomething();
std::shared_ptr<NoMoveClass> b = a; // also move a to b by copy pointer.
return 0;
}
Is it a good habit to always use the 2nd one?
Why many libraries, STL use the 1st one, not the 1st one ?
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