> new-expression:
> [::] new [placement] new-type-name [new-initializer]
> [::] new [placement] ( type-name ) [new-initializer]
>
> И далее
>
> placement
>     Provides a way of passing additional arguments
>     if you overload new.
>     (Создает возможность передачи дополнительных аргументов
>      в случае если вы перегружаете оператор new)
>

Where most other software documentation tends to to oscillate between incomprehensibility and oversimplifying condescension, classic Unix documentation is written to be telegraphic but complete. It does not hold you by the hand, but it usually points in the right direction. The style assumes an active reader, one who is able to deduce obvious unsaid consequences of what is said, and who has the self-confidence to trust those deductions.

Unix programmers tend to be good at writing references, and most Unix documentation has the flavor of a reference or aide memoire for someone who thinks like the document-writer but is not yet an expert at his or her software. The results often look much more cryptic and sparse than they actually are. Read every word carefully, because whatever you want to know will probably be there, or deducible from what's there. Read every word carefully, because you will seldom be told anything twice.

18.4.1.3 Placement forms [lib.new.delete.placement]
1 These functions are reserved, a C++ program may not define functions that displace the versions in the
Standard C++ library (17.4.3).
void* operator new(std::size_t size, void* ptr) throw();
2 Returns: ptr.
3 Notes: Intentionally performs no other action.

1.1 Scope [intro.scope]
...
2 C++ is a general purpose programming language based on the C programming language as described in ISO/IEC 9899:1990 Programming languages – C (1.2). In addition to the facilities provided by C, C++ provides additional data types, classes, templates, exceptions, namespaces, inline functions, operator overloading, function name overloading, references, free store management operators, and additional library facilities.

> Как вызвать деструктор для подобного объекта?

D>>Есть участок памяти, есть экземпяр объекта.
D>>Каким образом можно сконструировать объект — копию заданного объекта
D>>в заданном участке памяти (через конструктор копирования)?
CS>Примерно так

CS> void *p = ...;
CS> myclass * myclass_dst_object_p = new(p) myclass( myclass_src_object );

// This will call ::operator new(size_t, char*, int).
A* pa2 = new(__FILE__, __LINE__) A(20);

D>// This will call ::operator new(size_t, char*, int).
D>A* pa2 = new(__FILE__, __LINE__) A(20);

void* ::operator new(void* p, size_t /*который игнорируем*/) { /*здесь ничего не делаем*/ return p; }

D>в заданном участке памяти (через конструктор копирования)?

 void *p = ...;

 myclass * myclass_dst_object_p = new(p) myclass( myclass_src_object );

[lib.new.delete.placement]
18.4.1.3 Placement forms
1 These functions are reserved, a C++ program may not define functions that displace the versions in the Standard C++ library (17.4.3).

new-expression: 
[::] new [placement] new-type-name [new-initializer]
[::] new [placement] ( type-name ) [new-initializer] 

И далее

placement 
    Provides a way of passing additional arguments 
    if you overload new.
    (Создает возможность передачи дополнительных аргументов
     в случае если вы перегружаете оператор new)

D>Как вызвать деструктор для подобного объекта?

#include <new>
#include <boost/aligned_storage.hpp>

struct T {}; // это самый обобщенный тип на свете :)

int main()
{
    boost::aligned_storage<sizeof(T)> buf;
    void* ptr = buf.address();
    T* p = new(ptr) T;
    p->~T();
}

A>#include <new>
A>#include <boost/aligned_storage.hpp>

A>struct T {}; // это самый обобщенный тип на свете :)

A>int main()
A>{
A>    boost::aligned_storage<sizeof(T)> buf;
A>    void* ptr = buf.address();
A>    T* p = new(ptr) T;
A>    p->~T();
A>}

#include <new>
#include <boost/aligned_storage.hpp>

template<class T>
void foo()
{
    boost::aligned_storage<sizeof(T)> buf;
    void* ptr = buf.address();
    T* p = new(ptr) T;
    p->~T(); // TODO: RAII прикрутить?
}

struct X {};

int main()
{
    foo<X>();
}