On Tuesday, 12 August 2014 at 14:26:46 UTC, Jonathan M Davis via
Digitalmars-d-learn wrote:
AFAIK, the only time that the implicit conversion would take
place is when the
type is being used in a situation where it doesn't work
directly but where the
aliased type is used. In that case, the compiler sees the
accepted types and
sees that the type can implicitly convert to one of the
accepted types and
thus does the conversion. So, it knows that the conversion will
work before it
even does it. The compiler never attempts to do the conversion
just to see
whether it will work, which is essentially what it would have
to do when
attempting to use the type with a templated function. You can
certainly create
an enhancement request for such behavior, but I have no idea
how likely it is
get implemented. There are currently _no_ cases where the
compiler does
anything with template instantiations to try and make them pass
if simply
trying to instantiate them with the given type failed.
- Jonathan M Davis
What I mean is that this breaks the Liskov Substitution
Principle, which alias this should obey, as it denotes a subtype.
Since S!float has an alias this to float, it should behave as a
float in all circumstances where a float is expected; otherwise,
we've got a big problem with alias this on our hands.
