On Sunday, May 12, 2002, at 02:18 PM, Miko O'Sullivan wrote:
>> While thinking Eiffel-ish thoughts the other day, I began to wonder if
>> Perl6's classes could go beyond the simple private/public/protected
>> scheme by optionally allowing for a property or method to only be
>> accessed by a certain set of classes.
>
> Many times when I've used OO languages I've wished for something like
> this.
> What I've often wanted would be standard method that is called before
> every
> subroutine call. If that method returns false then the method that was
> called is not called.
I think maybe what you're looking for is another Eiffel/Sather-ism. I
know Eiffel at least has both pre and post-conditions that look
something like this(it's been a while, so if this isn't quite right):
class
ACCOUNT
creation
make_with_balance
feature { BANK }
balance: INTEGER
make_with_balance(initial_balance: INTEGER) is
require
initial_balance >= 0
do
balance := initial_balance
ensure
balance >= 0
end
end
I too have thought this might be useful in Perl6. Perhaps...
class Account {
my INT $balance;
method new(INT $initial_balance //= 0) {
REQUIRE { $initial_balance >= 0; }
$.balance = $initial_balance;
ENSURE { $.balance >= 0; }
}
}
