basically DiffMessage has a "take everything" ctor, which happens
to match on type DiffMessage itslef, since the latter is obviously
a Lumiera Forward Operator. Unfortunately the compiler now considers
this "take everyting" ctor as copy constructor. Worse even, such a
template generated ctor qualifies as "best match".
The result was, when just returing a DiffMessage by value form a
function, this erroneous "copy" operation was invoked, thus wrapping
the existing implementation into a WrappedLumieraIterator.
The only tangible symptom of this unwanted storage bloat was the fact
that our already materialised diagnostics where seemingly "gone". Indee
they weren't gone for real, just covered up under yet another layer of
DiffMessage wrapping another Lumiera Forward Iterator
Ichthyostega
b45ffe5cbe