Perl语言列表的true值和false值
示例
use feature qw( say ); # Numbers are true if they're not equal to 0. say 0 ? 'true' : 'false'; # false say 1 ? 'true' : 'false'; # true say 2 ? 'true' : 'false'; # true say -1 ? 'true' : 'false'; # true say 1-1 ? 'true' : 'false'; # false say 0e7 ? 'true' : 'false'; # false say -0.00 ? 'true' : 'false'; # false # Strings are true if they're not empty. say 'a' ? 'true' : 'false'; # true say 'false' ? 'true' : 'false'; # true say '' ? 'true' : 'false'; # false # Even if a string would be treated as 0 in numeric context, it's true if nonempty. # The only exception is the string "0", which is false. # To force numeric context add 0 to the string say '0' ? 'true' : 'false'; # false say '0.0' ? 'true' : 'false'; # true say '0e0' ? 'true' : 'false'; # true say '0 but true' ? 'true' : 'false'; # true say '0 whargarbl' ? 'true' : 'false'; # true say 0+'0 argarbl' ? 'true' : 'false'; # false # Things that become numbers in scalar context are treated as numbers. my @c = (); my @d = (0); say @c ? 'true' : 'false'; # false say @d ? 'true' : 'false'; # true # Anything undefined is false. say undef ? 'true' : 'false'; # false # References are always true, even if they point at something false my @c = (); my $d = 0; say \@c ? 'true' : 'false'; # true say \$d ? 'true' : 'false'; # true say \0 ? 'true' : 'false'; # true say \'' ? 'true' : 'false'; # true
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