I started to really like C#'s ?? operator. And I am quite used to the fact, that where there is something handy in some language, it's most probably in Perl too.
我开始真的很喜欢C＃了？运营商。我已经习惯了这样一个事实，即在某种语言中有一些方便的东西，它最有可能在Perl中。
However, I cannot find ?? equivalent in Perl. Is there any?
但是，我找不到??相当于Perl。有没有？
5 个解决方案
#1
30
As of 5.10 there is the // operator, which is semantically equivalent if you consider the concept of undef in Perl to be equivalent to the concept of null in C#.
从5.10开始，有//运算符，如果你认为Perl中的undef概念等同于C＃中的null概念，那么它在语义上是等价的。
Example A:
例A：
my $a = undef;
my $b = $a // 5; # $b = 5;
Example B:
例B：
my $a = 0;
my $b = $a // 5; # $b = 0;
#2
6
As Adam says, Perl 5.10 has the // operator that tests its lefthand operator for defined-ness instead of truth:
正如Adam所说，Perl 5.10有//运算符测试其左手操作符的定义而不是真相：
use 5.010;
my $value = $this // $that;
If you are using an earlier version of Perl, it's a bit messy. The || won't work:
如果您使用的是早期版本的Perl，则会有点混乱。 ||不会起作用：
my $value = $this || $that;
In that case, if $this is 0 or the empty string, both of which are defined, you'll get $that. To get around that, the idiom is to use the conditional operator so you can make your own check:
在这种情况下，如果$ this为0或空字符串（两者都已定义），您将得到$ that。为了解决这个问题，成语是使用条件运算符，这样你就可以自己检查：
my $value = defined( $this ) ? $this : $that;
#3
2
Actually, the short-circuit OR operator will also work when evaluating undef:
实际上，在评估undef时，短路OR运算符也可以工作：
my $b = undef || 5; # $b = 5;
However, it will fail when evaluating 0 but true:
但是，在评估0时它会失败但是为真：
my $b = 0 || 5; # $b = 5;
#4
0
The question implied any number of arguments, so the answer implies a subroutine :
这个问题暗示了任意数量的参数，所以答案意味着一个子程序：
Here you get it - will return the first defined/non empty-string value of a list :
在这里你得到它 - 将返回列表的第一个已定义/非空字符串值：
sub coalesce { (grep {length} @_)[0] }
#5
-4
Not that I know of.
从来没听说过。
Perl isn't really a big user of the null concept. It does have a test for whether a variable is undefined. No special operator like the ?? though, but you can use the conditional ?: operator with an undef test and get pretty close.
Perl实际上并不是null概念的大用户。它确实测试变量是否未定义。没有特殊的操作员喜欢??但是，您可以使用带有undef测试的条件？：运算符并且非常接近。
And I don't see anything in the perl operator list either.
我也没有在perl运算符列表中看到任何内容。
#1
30
As of 5.10 there is the // operator, which is semantically equivalent if you consider the concept of undef in Perl to be equivalent to the concept of null in C#.
从5.10开始，有//运算符，如果你认为Perl中的undef概念等同于C＃中的null概念，那么它在语义上是等价的。
Example A:
例A：
my $a = undef;
my $b = $a // 5; # $b = 5;
Example B:
例B：
my $a = 0;
my $b = $a // 5; # $b = 0;
#2
6
As Adam says, Perl 5.10 has the // operator that tests its lefthand operator for defined-ness instead of truth:
正如Adam所说，Perl 5.10有//运算符测试其左手操作符的定义而不是真相：
use 5.010;
my $value = $this // $that;
If you are using an earlier version of Perl, it's a bit messy. The || won't work:
如果您使用的是早期版本的Perl，则会有点混乱。 ||不会起作用：
my $value = $this || $that;
In that case, if $this is 0 or the empty string, both of which are defined, you'll get $that. To get around that, the idiom is to use the conditional operator so you can make your own check:
在这种情况下，如果$ this为0或空字符串（两者都已定义），您将得到$ that。为了解决这个问题，成语是使用条件运算符，这样你就可以自己检查：
my $value = defined( $this ) ? $this : $that;
#3
2
Actually, the short-circuit OR operator will also work when evaluating undef:
实际上，在评估undef时，短路OR运算符也可以工作：
my $b = undef || 5; # $b = 5;
However, it will fail when evaluating 0 but true:
但是，在评估0时它会失败但是为真：
my $b = 0 || 5; # $b = 5;
#4
0
The question implied any number of arguments, so the answer implies a subroutine :
这个问题暗示了任意数量的参数，所以答案意味着一个子程序：
Here you get it - will return the first defined/non empty-string value of a list :
在这里你得到它 - 将返回列表的第一个已定义/非空字符串值：
sub coalesce { (grep {length} @_)[0] }
#5
-4
Not that I know of.
从来没听说过。
Perl isn't really a big user of the null concept. It does have a test for whether a variable is undefined. No special operator like the ?? though, but you can use the conditional ?: operator with an undef test and get pretty close.
Perl实际上并不是null概念的大用户。它确实测试变量是否未定义。没有特殊的操作员喜欢??但是，您可以使用带有undef测试的条件？：运算符并且非常接近。
And I don't see anything in the perl operator list either.
我也没有在perl运算符列表中看到任何内容。