Re: AW: defining 'constants' at run time

[David Nicol]

Simon Cozens wrote:

[EMAIL PROTECTED] (Jochen Stenzel) writes:
 

the base technique is to build a "use constant" statement at runtime and evaluate it via eval().
   

% perl -w -Mstrict -le 'eval "use constant FOO => 3"; print FOO' 
Name "main::FOO" used only once: possible typo at -e line 1.
print() on unopened filehandle FOO at -e line 1.
%

Any other ideas?

you obviously can't compile the code you want the constants to be in 
until after you
have defined them -- otherwise they're not constants -- so define the 
constants before
you compile the code that sees them

perl -w -Mstrict -le 'BEGIN{eval "use constant FOO => 3"}; print FOO'
3
and if you don't really want a constant but rather an undecorated scalar 
that
won't interpolate, there is always the empty prototype.  I like to think of
C<use constant> as a shorthand for creating constant subroutines so I
generally just set up the constant subroutines when I need a named constant

perl -w -Mstrict -le 'BEGIN{eval "sub FOO(){3}"}; print FOO'
3
I wonder what aspect of "constant" is desired to be kept.  If it is lack
of decoration,
Furthermore,
perl -w -Mstrict -le 'sub FOO(){3}; print FOO; *FOO = sub(){4}; print FOO'
3
Constant subroutine main::FOO redefined at -e line 1.
3
but folding can be suppressed
perl -w -Mstrict -le 'sub FOO(){my$x; 3}; print FOO; *FOO = sub(){4}; 
print FOO'
3
Subroutine main::FOO redefined at -e line 1.
4



--
[EMAIL PROTECTED]
Include phrase "cat and buttered toast" to get through my filter