Hi,

while upgrading a project from rust_postgres 0.15 to 0.17 and r2d2_postgres 0.14 to 0.16, we have some troubles with the new definition ofPostgresConnectionManager<T> that contains a new generic parameter<T>.
The problem is that the r2d2 pool returns aPooledConnection that now has the very same generic parameter<T> that, as a consequence, has to be redeclared in every place where the connection is used.

For example, our project structure follows the Domain Driven Design principle, then:

• we have a set of Repositories that use aPooledConnection, so they all have to declare the<T> generic param
• we have a set of Services that use the Repositories, so all Services need to declare<T> too
• we have a set of Controllers that use the Services, so all Controllers need to declare<T>
• and so on...

In the end, this<T> generic is declared literally everywhere.

In addition, the rust_postgresClient has no generic parameters at all so it is not clear why thePooledConnection requires it.

I don't know if it is feasible, but the issue could be fixed by changing the signature in the r2d2 pool from:

pubfnget(&self) ->Result<PooledConnection<M>,Error>;

to

pubfnget(&self) ->Result<PooledConnection<M::Connection>,Error>;

Or, maybe, the<T> param can be boxed in thePostgresConnectionManager struct:

#[derive(Debug)]pubstructPostgresConnectionManager{config:Config,tls_connector:Box<MakeTlsConnect<Socket,TlsConnect=Send,Stream=Send, ... >>,}