Makes sense to me.

(The only way i can think of that it might work, is if the is SomeClass attribute of a parameter indicates that an exception should be thrown if something other then SomeClass is passed in -- but that seems like a non-standard use of the "is" keyword)

That's pretty much how it works (as I understand it), but it's only a side-effect of the fact that you're giving the parameter a type. That is, it's standard in the same way that: 

my SomeClass $foo;                # a.k.a.  my $foo is SomeClass;
my SomeOtherClass $bar = stuff();
$foo = $bar;                      # compile-time exception

[download]

producing an exception is standard when SomeOtherClass is not a child of SomeClass. It just has the benefit of letting us make the compiler enforce some of the "correctness" of the passed values.

Again, this is just how I understand it from the Exegesis and Apocolypse. I could be horribly wrong, of course. :)

Update: Re: The sub parameter being an alias. Am I correct in remembering that one of the Apocolypses indicated that the properties (such as type; or it may have just been the type) are properties of the name we give the variables, and not the actual value/container? This is why the fact that the parameter is just an alias doesn't bother me.

bbfu
Black flowers blossom
Fearless on my breath

In reply to Re: Ex6: Using "is" on aliased sub parameters? by bbfu
in thread Ex6: Using "is" on aliased sub parameters? by hossman

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.