问题描述
Perl 6似乎有相等运算符的爆炸式增长.什么是=:=? leg和cmp有什么区别?还是eqv和===?
Perl 6 seems to have an explosion of equality operators. What is =:=? What's the difference between leg and cmp? Or eqv and ===?
有人总结不错吗?
推荐答案
=:= 测试两个容器(变量或数组项或哈希项)是否被别名，即，如果其中一个发生变化，另一个容器是否也发生变化?
=:= tests if two containers (variables or items of arrays or hashes) are aliased, ie if one changes, does the other change as well?
my $x;
my @a = 1, 2, 3;
# $x =:= @a[0] is false
$x := @a[0];
# now $x == 1, and $x =:= @a[0] is true
$x = 4;
# now @a is 4, 2, 3
对于其他: === 测试是否有两个引用指向到同一个对象，然后 eqv 测试两个对象在结构上是否等效.因此[1, 2, 3] === [1, 2, 3]将为false(不是相同的数组)，但[1, 2, 3] eqv [1, 2, 3]将为true(相同的结构).
As for the others: === tests if two references point to the same object, and eqv tests if two things are structurally equivalent. So [1, 2, 3] === [1, 2, 3] will be false (not the same array), but [1, 2, 3] eqv [1, 2, 3] will be true (same structure).
leg比较Perl 5的cmp之类的字符串，而Perl 6的cmp则更聪明，并且将比较<=>之类的数字和leg之类的字符串.
leg compares strings like Perl 5's cmp, while Perl 6's cmp is smarter and will compare numbers like <=> and strings like leg.
13 leg 4 # -1, because 1 is smaller than 4, and leg converts to string
13 cmp 4 # +1, because both are numbers, so use numeric comparison.
最后，~~是智能匹配"，它回答了问题是否$x匹配$y".如果$y是类型，则为类型检查.如果$y是正则表达式，则为正则表达式匹配-依此类推.
Finally ~~ is the "smart match", it answers the question "does $x match $y". If $y is a type, it's type check. If $y is a regex, it's regex match - and so on.
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