[Perl5-syntax] How to test for a role in a method signature

[Michael G Schwern]

On 2011.3.9 7:13 AM, Buddy Burden wrote:
>> We could call them types if types didn't already mean something specific in
>> Moose.
> 
> But what it specifically means is what we're talking about, right?
> Whether applied to an attribute or a method parameter, a "type" in
> Moose is merely a constraint on what can and cannot be assigned to it.
> What we tend to call "types" (Int, Str, Num, and so forth) are
> actually more like predefined constraints ... a subset of all the
> possible types.
> 
> At least that's my take on it.

Ahh.  I see it the other way around.  Int, Str, Num and all are types as
opposed to classes.  And then Moose's has => isa takes a type or a class.

Looking at the Moose docs, I guess they make it clear that they're not types
but "type constraints", though I think that distinction is lost on most.
"Predefined constraint" is also accurate


>>> We could refer to them as "constraints" I suppose ... type
>>> constraints, class constraints, and role constraints. <shrug>
>>
>> Technically they are a constraint, but "where" is already called constraints,
>> and that lines up with vocabulary in other languages like SQL.
> 
> That's true.  Although all types devolve to a "where" underneath.  But
> I see the value in making a distinction, sure.

True.  You are right that "constraint" is the proper generic term.

Call them all "constraints" with the thing on the left a "type constraint" and
the thing on the right a "free form constraint"?  Or less correctly but more
usefully, a "where constraint".


-- 
We do what we must because we can.
For the good of all of us,
Except the ones who are dead.
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