(j3.2006) Why did we do this?

[Van Snyder]

[10-007r1:217:22] says "If an input or output item {in an I/O list} is 
allocatable it shall be allocated."

[218:1-5] goes on "If an item of derived type ... the list item is 
treated as if all of the components of the object were specified in the 
list in component order; those components ... shall not be pointers or 
allocatable."

If the program listed the components explicitly, the allocatable or 
pointer ones would be allowed.  If the processor splits them out into 
components in component order, they're not allowed.

Why did we do this?

I do see a problem with I/O for derived type objects with allocatable 
pointer components, the problem being that the processor doesn't 
automatically split the object into its components if any of the 
components are pointer or allocatable.  It only does this if any 
component would be processed by a defined I/O procedure.

If objects of derived type were treated as a list of their components, 
in component order, if any of them are pointers or allocatable, the 
problem goes away?

Why did we do this?

We didn't prohibit objects of types with length components from 
appearing in I/O lists.