a temporary object in range_based for loop related question in c-CodePudding

in this page Range-based for loop on a temporary range, user Barry mentioned that the following is not affected by the destroyed temporary object, and I tested member v indeed exists throughout the for loop(as the destructor ~X didn't get called throughout the for loop). Can anyone explain why for me please? Many thanks!

struct X {
    std::vector<int> v;
    ~X()
    {
    }
};
X foo()
{
return X();
}

for (auto e : foo().v) {
    // ok!
}

CodePudding user response：

This is an obscure form of temporary lifetime extension. Normally you have to bind the temporary directly to the reference for it to work (e.g. for (auto x : foo())), but according to cppreference, this effect propagates through:

parentheses ( ) (grouping, not a function call),
array access [ ],
member access ., .*,
ternary operator ? :
comma operator ,.
any cast that doesn't involve a "user-defined conversion" (presumably uses no constructors nor conversion operators)

I.e. if a.b is bound to a reference, the lifetime of a is extended.