I never contributed to boost, I'm not sure what kind of test I should write for this? For now, I ran successfully b2 in boost/libs/container/test with this patch applied.
This patch adds a variant of map constructors to avoid useless extra allocator copy when using initializer list
Many existing constructors have this form:
map(std::initializer_list il, const Compare& comp = Compare(), const allocator_type& a = allocator_type())
The issue is that a temporary allocator_type is constructed, and
passed to the base class where it is used to copy-constructed the
rebound allocator.
This temporary allocator_type here is always destroyed at the end
of the map() constructor. For stateful allocators this is not
desirable.
The solution is to adopt what libc++ is doing and have to constructors:
map(std::initializer_list il, const Compare& comp = Compare(), const allocator_type& a)
and
map(std::initializer_list il, const Compare& comp = Compare())
This way, unless an allocator is provided by the client, no extra temporary
creation/destruction occurs.
I never contributed to boost, I'm not sure what kind of test I should write for this? For now, I ran successfully b2 in
boost/libs/container/test
with this patch applied.This patch adds a variant of map constructors to avoid useless extra allocator copy when using initializer list
Many existing constructors have this form:
map(std::initializer_list il, const Compare& comp = Compare(), const allocator_type& a = allocator_type())
The issue is that a temporary allocator_type is constructed, and passed to the base class where it is used to copy-constructed the rebound allocator. This temporary allocator_type here is always destroyed at the end of the map() constructor. For stateful allocators this is not desirable. The solution is to adopt what libc++ is doing and have to constructors:
map(std::initializer_list il, const Compare& comp = Compare(), const allocator_type& a)
and
map(std::initializer_list il, const Compare& comp = Compare())
This way, unless an allocator is provided by the client, no extra temporary creation/destruction occurs.