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c++lambdathisinitializer

Can anybody explain this initializer code?

Can anybody explain how "self_( this, []( ... ) {} )" works?

struct Parent {
    std::shared_ptr<Parent> self_;
    Parent() : self_( this, []( ... ) {} ) {}
    operator std::shared_ptr<Parent>() const { return self_; }
}
Solution

  • Can anybody explain how "self_( this, []( ... ) {} )" works?

    self_, member of Parent, is a std::shared_ptr<Parent>.

    With 

    self_( this, []( ... ) {} )

    is initialized using a constructor with two arguments:

    (1) the pointer shared, this, a pointer to the same object containing self_ (so the name)

    (2) the function that is called when the self_ object is deleted

    Observe the function: []( ... ) {}

    It's a lambda function that can accept all (..., the old-C variadic way) and do nothing (the body is empty).

    This (the do-nothing deleter) is done because when the last shared pointer with a specific value is destroyed, nothing has to be done over a this pointer.