package constant;
use strict;
-use 5.005_64;
+use 5.006_00;
use warnings::register;
our($VERSION, %declared);
-$VERSION = '1.02';
+$VERSION = '1.04';
#=======================================================================
sub import {
my $class = shift;
return unless @_; # Ignore 'use constant;'
- my $name = shift;
- unless (defined $name) {
- require Carp;
- Carp::croak("Can't use undef as constant name");
+ my %constants = ();
+ my $multiple = ref $_[0];
+
+ if ( $multiple ) {
+ if (ref $_[0] ne 'HASH') {
+ require Carp;
+ Carp::croak("Invalid reference type '".ref(shift)."' not 'HASH'");
+ }
+ %constants = %{+shift};
+ } else {
+ $constants{+shift} = undef;
}
- my $pkg = caller;
-
- # Normal constant name
- if ($name =~ /^_?[^\W_0-9]\w*\z/ and !$forbidden{$name}) {
- # Everything is okay
-
- # Name forced into main, but we're not in main. Fatal.
- } elsif ($forced_into_main{$name} and $pkg ne 'main') {
- require Carp;
- Carp::croak("Constant name '$name' is forced into main::");
-
- # Starts with double underscore. Fatal.
- } elsif ($name =~ /^__/) {
- require Carp;
- Carp::croak("Constant name '$name' begins with '__'");
-
- # Maybe the name is tolerable
- } elsif ($name =~ /^[A-Za-z_]\w*\z/) {
- # Then we'll warn only if you've asked for warnings
- if (warnings::enabled()) {
- if ($keywords{$name}) {
- warnings::warn("Constant name '$name' is a Perl keyword");
- } elsif ($forced_into_main{$name}) {
- warnings::warn("Constant name '$name' is " .
- "forced into package main::");
+
+ foreach my $name ( keys %constants ) {
+ unless (defined $name) {
+ require Carp;
+ Carp::croak("Can't use undef as constant name");
+ }
+ my $pkg = caller;
+
+ # Normal constant name
+ if ($name =~ /^_?[^\W_0-9]\w*\z/ and !$forbidden{$name}) {
+ # Everything is okay
+
+ # Name forced into main, but we're not in main. Fatal.
+ } elsif ($forced_into_main{$name} and $pkg ne 'main') {
+ require Carp;
+ Carp::croak("Constant name '$name' is forced into main::");
+
+ # Starts with double underscore. Fatal.
+ } elsif ($name =~ /^__/) {
+ require Carp;
+ Carp::croak("Constant name '$name' begins with '__'");
+
+ # Maybe the name is tolerable
+ } elsif ($name =~ /^[A-Za-z_]\w*\z/) {
+ # Then we'll warn only if you've asked for warnings
+ if (warnings::enabled()) {
+ if ($keywords{$name}) {
+ warnings::warn("Constant name '$name' is a Perl keyword");
+ } elsif ($forced_into_main{$name}) {
+ warnings::warn("Constant name '$name' is " .
+ "forced into package main::");
+ } else {
+ # Catch-all - what did I miss? If you get this error,
+ # please let me know what your constant's name was.
+ # Write to <rootbeer@redcat.com>. Thanks!
+ warnings::warn("Constant name '$name' has unknown problems");
+ }
+ }
+
+ # Looks like a boolean
+ # use constant FRED == fred;
+ } elsif ($name =~ /^[01]?\z/) {
+ require Carp;
+ if (@_) {
+ Carp::croak("Constant name '$name' is invalid");
} else {
- # Catch-all - what did I miss? If you get this error,
- # please let me know what your constant's name was.
- # Write to <rootbeer@redcat.com>. Thanks!
- warnings::warn("Constant name '$name' has unknown problems");
+ Carp::croak("Constant name looks like boolean value");
}
- }
- # Looks like a boolean
- # use constant FRED == fred;
- } elsif ($name =~ /^[01]?\z/) {
- require Carp;
- if (@_) {
- Carp::croak("Constant name '$name' is invalid");
} else {
- Carp::croak("Constant name looks like boolean value");
+ # Must have bad characters
+ require Carp;
+ Carp::croak("Constant name '$name' has invalid characters");
}
- } else {
- # Must have bad characters
- require Carp;
- Carp::croak("Constant name '$name' has invalid characters");
- }
-
- {
- no strict 'refs';
- my $full_name = "${pkg}::$name";
- $declared{$full_name}++;
- if (@_ == 1) {
- my $scalar = $_[0];
- *$full_name = sub () { $scalar };
- } elsif (@_) {
- my @list = @_;
- *$full_name = sub () { @list };
- } else {
- *$full_name = sub () { };
+ {
+ no strict 'refs';
+ my $full_name = "${pkg}::$name";
+ $declared{$full_name}++;
+ if ($multiple) {
+ my $scalar = $constants{$name};
+ *$full_name = sub () { $scalar };
+ } else {
+ if (@_ == 1) {
+ my $scalar = $_[0];
+ *$full_name = sub () { $scalar };
+ } elsif (@_) {
+ my @list = @_;
+ *$full_name = sub () { @list };
+ } else {
+ *$full_name = sub () { };
+ }
+ }
}
}
-
}
1;
print CCODE->("me");
print CHASH->[10]; # compile-time error
+ # declaring multiple constants at once
+ use constant {
+ BUFFER_SIZE => 4096,
+ ONE_YEAR => 365.2425 * 24 * 60 * 60,
+ PI => 4 * atan2( 1, 1 ),
+ DEBUGGING => 0,
+ ORACLE => 'oracle@cs.indiana.edu',
+ USERNAME => scalar getpwuid($<), # this works
+ USERINFO => getpwuid($<), # THIS IS A BUG!
+ };
+
=head1 DESCRIPTION
This will declare a symbol to be a constant with the given scalar
Constant symbols are package scoped (rather than block scoped, as
C<use strict> is). That is, you can refer to a constant from package
-Other as C<Other::CONST>.
+Other as C<Other::CONST>. You may also use constants as either class
+or object methods, ie. C<< Other->CONST() >> or C<< $obj->CONST() >>.
+Such constant methods will be inherited as usual.
As with all C<use> directives, defining a constant happens at
compile time. Thus, it's probably not correct to put a constant
declaration inside of a conditional statement (like C<if ($foo)
-{ use constant ... }>).
+{ use constant ... }>). When defining multiple constants, you
+cannot use the values of other constants within the same declaration
+scope. This is because the calling package doesn't know about any
+constant within that group until I<after> the C<use> statement is
+finished.
+
+ use constant {
+ AGE => 20,
+ PERSON => { age => AGE }, # Error!
+ };
+ [...]
+ use constant PERSON => { age => AGE }; # Right
-Omitting the value for a symbol gives it the value of C<undef> in
-a scalar context or the empty list, C<()>, in a list context. This
-isn't so nice as it may sound, though, because in this case you
-must either quote the symbol name, or use a big arrow, (C<=E<gt>>),
-with nothing to point to. It is probably best to declare these
-explicitly.
+Giving an empty list, C<()>, as the value for a symbol makes it return
+C<undef> in scalar context and the empty list in list context.
- use constant UNICORNS => ();
- use constant LOGFILE => undef;
+ use constant UNICORNS => ();
-The result from evaluating a list constant in a scalar context is
-not documented, and is B<not> guaranteed to be any particular value
-in the future. In particular, you should not rely upon it being
-the number of elements in the list, especially since it is not
-B<necessarily> that value in the current implementation.
+ print "Impossible!\n" if defined UNICORNS;
+ my @unicorns = UNICORNS; # there are no unicorns
-Magical values, tied values, and references can be made into
-constants at compile time, allowing for way cool stuff like this.
-(These error numbers aren't totally portable, alas.)
+The same effect can be achieved by omitting the value and the big
+arrow entirely, but then the symbol name must be put in quotes.
+
+ use constant "UNICORNS";
+
+The result from evaluating a list constant with more than one element
+in a scalar context is not documented, and is B<not> guaranteed to be
+any particular value in the future. In particular, you should not rely
+upon it being the number of elements in the list, especially since it
+is not B<necessarily> that value in the current implementation.
+
+Magical values and references can be made into constants at compile
+time, allowing for way cool stuff like this. (These error numbers
+aren't totally portable, alas.)
use constant E2BIG => ($! = 7);
print E2BIG, "\n"; # something like "Arg list too long"
print 0+E2BIG, "\n"; # "7"
+You can't produce a tied constant by giving a tied scalar as the
+value. References to tied variables, however, can be used as
+constants without any problems.
+
Dereferencing constant references incorrectly (such as using an array
subscript on a constant hash reference, or vice versa) will be trapped at
compile time.
+When declaring multiple constants, all constant values B<must be
+scalars>. If you accidentally try to use a list with more (or less)
+than one value, every second value will be treated as a symbol name.
+
+ use constant {
+ EMPTY => (), # WRONG!
+ MANY => ("foo", "bar", "baz"), # WRONG!
+ };
+
+This will get interpreted as below, which is probably not what you
+wanted.
+
+ use constant {
+ EMPTY => "MANY", # oops.
+ foo => "bar", # oops!
+ baz => undef, # OOPS!
+ };
+
+This is a fundamental limitation of the way hashes are constructed in
+Perl. The error messages produced when this happens will often be
+quite cryptic -- in the worst case there may be none at all, and
+you'll only later find that something is broken.
+
In the rare case in which you need to discover at run time whether a
particular constant has been declared via this module, you may use
this function to examine the hash C<%constant::declared>. If the given
Tom Phoenix, E<lt>F<rootbeer@redcat.com>E<gt>, with help from
many other folks.
+Multiple constant declarations at once added by Casey West,
+E<lt>F<casey@geeknest.com>E<gt>.
+
+Assorted documentation fixes by Ilmari Karonen,
+E<lt>F<perl@itz.pp.sci.fi>E<gt>.
+
=head1 COPYRIGHT
Copyright (C) 1997, 1999 Tom Phoenix
projects / p5sagit/p5-mst-13.2.git / blobdiff