The new types in base/ram.h model different allocation scenarios and
error cases by mere C++ types without using exceptions. They are meant
to replace the former 'Ram_allocator' interface. As of now, the
'Unmapped_allocator' closely captures the former 'Ram_allocator'
semantics. The 'Constrained_allocator' is currently an alias for
'Unmapped_allocator' but is designated for eventually allocating
mapped RAM.
In contrast to the 'Ram_allocator' interface, which talked about
dataspace capabilites but left the lifetime management of the
allocated RAM to the caller, the new API represents an allocation
as a guard type 'Allocation', which deallocates on destruction by
default.
Allocation errors are captured by a 'Result' type that follows
the 'Attempt' pattern.
As a transitionary feature, the patch largely maintains API
compatibility with the original 'Ram_allocator' by providing
the original (exception-based) 'Ram_allocator::alloc' and
'Ram_allocator::free' methods as a wrapper around the new
'Ram::Constrained_allocator'. So components can be gradually
updated to the new 'Ram::' interface.
Issue #5502
The 'Allocation' type represents the result of an allocator, which
guards the lifetime of the allocation. The 'Allocation::Attempt' type is
a suitable result type for allocators that need to reflect either an
successful allocation or an error condition.
Issue #5502
