This and other RFCs are available on the web at
http://dev.perl.org/rfc/
=head1 TITLE
Variable interpolation on demand.
=head1 VERSION
Maintainer: Glenn Linderman <[EMAIL PROTECTED]>
Date: 14 Sep 2000
Mailing List: [EMAIL PROTECTED]
Number: 229
Version: 1
Status: Developing
=head1 ABSTRACT
Make Perl's powerful string interpolation facilities are available to
variables, in addition to literals.
=head1 DESCRIPTION
Given:
$foo = 'def';
$bar = 'ghi';
$x = "abc$foo$bar";
$y = 'abc$foo$bar';
There is no way to turn obtain the value of $x from the value of $y.
In other words, while $foo and $bar were interpolated into $x, they
were not interpolated into $y. It would be nice to get Success! from:
$z = interpolate ( $y );
print 'Success!" if $z eq $x;
However, there is no direct language facility for this, because
interpolation only happens one level deep (which is good), so attempts
such as
$z = qq/$y/;
will interpolate $y, but not $foo and $bar, so $z eq $y, instead of $z
eq $x.
Shown above is a functional syntax. However, due to scoping rules and
lexical variables, it is unlikely that this functionality could be
implemented as a function, more likely it would have to be a keyword.
An alternate syntax might be:
$z = qd/$y/;
implying a double interpolation pass. Or
$z = q2/$y/;
which means 2 interpolation passes, and which could be extended to q3,
q4, q5 ??? Or
$z = qq/$y/2;
which likewise would mean two passes, and could be extended to 3, 4, 5,
or even to
$z = qq/$y/$n;
a variable number of passes. The same could be achieved with the
keyword technique via an additional parameter:
interpolate ( $y, $n );
=head2 Compatibility considerations
This is a new feature, so name conflict is the only issue.
=head1 IMPLEMENTATION
Just a re-write rule.
=head1 REFERENCES
None.
