From: Casey R. Tweten Date: Fri, 22 Dec 2000 10:35:53 +0000 (-0500) Subject: Re: [PATCH] Idea: Declare multiple constants at once X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=3cb88d136107e23d028d4e1fea0eb9147639fa8e;p=p5sagit%2Fp5-mst-13.2.git Re: [PATCH] Idea: Declare multiple constants at once Message-ID: p4raw-id: //depot/perl@8240 --- diff --git a/lib/constant.pm b/lib/constant.pm index 72ad793..1e07a68 100644 --- a/lib/constant.pm +++ b/lib/constant.pm @@ -28,75 +28,93 @@ my %forbidden = (%keywords, %forced_into_main); 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 '$name' is " . + "forced into package main::"); + } else { + # Catch-all - what did I miss? If you get this error, + # please let me know what your constant's name was. + # Write to . Thanks! + warnings::warn("Constant name '$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 . 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 { + *$full_name = sub () { }; + } + } } } - } 1; @@ -133,6 +151,17 @@ constant - Perl pragma to declare constants print CCODE->("me"); print CHASH->[10]; # compile-time error + # declaring multiple constants at once + use constant { + BUFFER_SIZE => 4096, + ONE_YEAR => 365.2425 * 24 * 60 * 60, + PI => 4 * atan2( 1, 1 ), + DEBUGGING => 0, + ORACLE => 'oracle@cs.indiana.edu', + USERNAME => scalar getpwuid($<), + USERINFO => getpwuid($<), + }; + =head1 DESCRIPTION This will declare a symbol to be a constant with the given scalar @@ -176,14 +205,26 @@ Other as C. As with all C 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). +{ 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 the C 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 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>), -with nothing to point to. It is probably best to declare these -explicitly. +with nothing to point to. It is also illegal to do when defining +multiple constants at once, you must declare them explicitly. It +is probably best to declare these explicitly. use constant UNICORNS => (); use constant LOGFILE => undef; @@ -206,6 +247,11 @@ 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 will be a scalar. +This is because C can't guess the intent of the programmer +correctly all the time since values must be expressed in scalar context +within a hash ref. + 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 @@ -268,6 +314,9 @@ C 'value'>. Tom Phoenix, EFE, with help from many other folks. +Multiple constant declarations at once added by Casey Tweten, +EFE. + =head1 COPYRIGHT Copyright (C) 1997, 1999 Tom Phoenix