bsl::allocator_traits::select_on_container_copy_construction

Return a copy of the allocator that should be used to copy‐ construct one container from another container whose allocator is the specified rhs. If the parameterized ALLOCATOR_TYPE defines a method select_on_container_copy_construction, this function returns the result of calling that method on rhs; otherwise, this method enforces the default policy of propagating the allocator on copy construction, as is standard practice for standard allocators (i.e., returns rhs). Note that the specialization of this class template for bsl::allocator (in the bslma_bslallocator component) provides the alternate default behavior of not propagating the allocator on copy construction (i.e., returning a default‐constructed allocator object).