For many allocations (and deallocations, when using sized delete), it would be profitable to inline the implementation.
The practical issues encountered due to the One Definition rule are discussed by [P1220].
Under 188.8.131.52 [replacement.functions], the ability to inline the replaceable functions used for allocation is forbidden ("The program’s declarations shall not be specified as inline. No diagnostic is required.").
This paper focuses on the ability to specify replaceable functions as inline. This restriction came about as the resolution to [LWG404], adopted at the Sydney meeting [N1629].
Wording is relative to [N4762].
The program’s declarations shall not be specified as inline. No diagnostic is required.