我试图找出在没有传递参数的情况和参数传递为0的情况下在Perl中区分的最佳方法,因为它们对我来说意味着不同的东西.
(通常我喜欢歧义,但在这种情况下我生成sql所以我想用NULL替换未定义的args,但将0保留为0)
所以这是含糊不清的：
sub mysub {
my $arg1 = shift;
if ($arg1){
print "arg1 could have been 0 or it could have not been passed.";
}
}
到目前为止,这是我最好的解决方案……但我认为这有点难看.我想知道你是否能想到一种更清洁的方式,或者这对你来说是否合适：
sub mysub {
my $arg1 = (defined shift) || "NULL";
if ($arg1 ne "NULL"){
print "arg1 came in as a defined value.";
}
else {
print "arg1 came in as an undefined value (or we were passed the string 'NULL')";
}
}
解决方法
以下是如何处理所有可能情况的示例：
sub mysub {
my ($arg1) = @_;
if (@_ < 1) {
print "arg1 wasn't passed at all.\n";
} elsif (!defined $arg1) {
print "arg1 was passed as undef.\n";
} elsif (!$arg1) {
print "arg1 was passed as a defined but false value (empty string or 0)\n";
} else {
print "arg1 is a defined,non-false value: $arg1\n";
}
}
(@_是函数的参数数组.这里将它与1进行比较是计算数组中元素的数量.我故意避免移位,因为它改变了@_,这将要求我们存储原始大小@_某处.)