IMPROVEMENTS:
1. Add explicit zero-argument overload to avoid SFINAE ambiguity
2. Require at least one argument (A1) for parameterized overloads
3. Better separation between direct initialization and aggregate initialization
BENEFITS:
- Clearer intent: zero-argument construction is explicitly handled
- Avoids potential SFINAE ambiguity when empty parameter pack is used
- More maintainable: easier to understand which overload is selected
- Consistent with modern C++ best practices for variadic templates
TECHNICAL DETAILS:
- Zero-arg overload: Always uses T() for value initialization
- One-or-more-arg overload: Uses SFINAE to choose between:
* T(args...) for types with matching constructor
* T{args...} for aggregate types or types with initializer_list ctor
This is a code quality improvement and does not fix any compilation issues,
but provides better template overload resolution.
ROOT CAUSE:
The allocate() function was incorrectly constructing objects during memory
allocation, violating C++ allocator requirements. MSVC's std::_Tree_node has
a deleted default constructor, causing compilation failure.
CHANGES:
- container_allocator::allocate() now only allocates raw memory without
constructing objects (removed mem::$new and ipc::construct calls)
- container_allocator::deallocate() now only frees memory without
destroying objects (removed mem::$delete and ipc::destroy_n calls)
WHY THIS FIXES THE ISSUE:
C++ allocator semantics require strict separation:
* allocate() -> raw memory allocation only
* construct() -> object construction with proper arguments
* destroy() -> object destruction
* deallocate() -> memory deallocation only
Standard containers (like std::map) call construct() with proper arguments
(key, value) to initialize nodes, not allocate(). Since std::_Tree_node in
MSVC has no default constructor (= delete), attempting to construct it
without arguments always fails.
Fixes MSVC 2017 compilation error:
error C2280: 'std::_Tree_node<...>::_Tree_node(void)':
attempting to reference a deleted function
