Forward link vs const lvalue in the template

Question

I recently studied link forwarding to C ++, and below is a summary of my current understanding of the concept.

Let's say I have a template function foothat translates a forwarding link to a single type argument T.

template<typename T>
void foo(T&& arg);

If I call this function with lvalue, then it Twill be output as T&if the parameter is of argtype T&due to the rules for dropping the link T& && -> T&.

If this function is called with an unnamed temporary, for example, the result of a function call, then it Twill be displayed as Tif the parameter is of argtype T&&.

Inside, foohowever arg, it is a named parameter, so I will need to use std::forwardit if I want to pass the parameter along with other functions and still maintain its category of values.

template<typename T>
void foo(T&& arg)
{
    bar(std::forward<T>(arg));
}

As far as I understand, cv qualifiers are not subject to this forwarding. This means that if I call foo with a named constant variable, it Twill be inferred as const T&, and therefore the type argwill also be const T&due to the rules for dropping the link. For const rvalues Twill be output as const Tand therefore argwill have a type const T&&.

It also means that if I change the value arginternally foo, I will get a compile-time error if I did infact by passing it a constant variable.

. , .

template<typename T>
class Container
{
public:
    void insert(T&& obj) { storage[size++] = std::forward<T>(obj); }
private:
    T *storage;
    std::size_t size;
    /* ... */
};

- insert obj, std::forward, T, insert infact .

, , -, const lvalue: void insert(const T& obj).

, ( ) , insert .

, .

- ? const lvalue, .

void insert(const T& obj);
void insert(T&& obj);

, std::vector , push_back .

void push_back (const value_type& val);
void push_back (value_type&& val);

( const value_type&)?

Answer 1

, . insert . .

Container<int> c;
c.insert(...);

, T , int, T , .

, , : , . , , ( STL ).

, , T int, :

void insert(int&& obj) { storage[size++] = std::forward<int>(obj); }

, rvalue, .. rvalues. , push_back, lvalues ​​ rvalues.

Answer 2

@ , .

Container ( , std::vector STL), , .

:

void insert(T const& t) {
    storage[size++] = t;
}
void insert(T && t) {
    storage[size++] = std::move(t);
}

, :

void insert(T t) {
    storage[size++] = std::move(t);
}

, , t , storage[size++], , t , storage[size++]. , -, .

, : - move ( ), , , ( , ), , , . , , . , , STL ( ). , , , " ", , , .