Re: [External] : Re: Remainder in pattern matching

[Brian Goetz]

Yes, and this is a special case of a more general thing -- that while 
pattern declarations may have a lot in common with methods, they are not 
"just methods with multiple return" (e.g., they have a different set of 
characteristics at the declaration, they are intrinsically conditional, 
they are "invoked" differently.)  While their bodies may look 
method-like, and ultimately they boil down to methods, thinking "they 
are just methods" is likely to drag you to the wrong place.  Of course, 
its a balance between how similar and HOW DIFFERENT they are, and that's 
what we're looking for.

Another thing it gains is that it discourages people
from thinking they can use exceptions in dtors; having these laundered
through MatchException discourages using this as a side channel, though
that's a more minor thing.
This is a stronger argument than you give it credit for being.
Wrapping the exception adds a bit of friction to doing the wrong thing
which will pay off in helping guide users to the intended behaviour.