Method do_allocate

test/doc_background.cpp:150–150

struct my_resource : container::pmr::memory_resource
{
    void* do_allocate  ( size_t, size_t ) override { return 0; }
    void  do_deallocate( void*, size_t, size_t ) override {}
    bool  do_is_equal  ( memory_resource const& ) const noexcept override { return true; }
};