Proposed resolution:

See N2424 for the proposed resolution.

[ Bellevue: ]

Close NAD for the reasons given in N2424. In practice it is not inconvenient to meet these requirements.

The requirement "P shall have a declaration of the form typedef X distribution_- type" effectively makes the use of inheritance for implementing distributions very inconvenient, because the child of a distribution class in general will not satisfy this requirement. In my opinion the benefits of having a typedef in the parameter class pointing back to the distribution class are not worth the hassle this requirement causes. [In my code base I never made use of the nested typedef but on several occasions could have profited from being able to use simple inheritance for the implementation of a distribution class.]

Proposed resolution: I propose to drop this requirement.