哪个上下文使此Perl 6 zip运算符感到困惑? [英] Which context confuses this Perl 6 zip operator?

问题描述

请考虑在我创建哈希的程序.然后，我要更改其中的两个值:

Consider this program where I create a hash. I want to then change two values in it:

my $hash = %(
    wallet   => 100,
    gave     =>   0,
    received =>   0,
    );

for ^1 { $hash<wallet gave> Z+= <-1 1> };

dd $hash;

像这样，for的最后一行不执行任何操作，也没有警告.哈希值保持不变:

Like this, the last line of for doesn't do anything and there is no warning. The hash is unchanged:

Hash $hash = ${:gave(0), :received(0), :wallet(100)}

添加另一条语句会更改行为:

Adding another statement changes the behavior:

my $hash = %(
    wallet   => 100,
    gave     =>   0,
    received =>   0,
    );

for ^1 { $hash<wallet gave> Z+= <-1 1>; True };

dd $hash;

现在就地编辑就可以了，但是有一个警告(尽管我发现无用"对它有用)

Now the inplace edit does its thing, but there's a warning (although I dispute "useless" when I've found a use for it):

Useless use of constant value True in sink context
Hash $hash = ${:gave(1), :received(0), :wallet(99)}

如果我没有Z+=，应该是同一件事，那么它会起作用:

If I do without the Z+=, which should be the same thing, it works:

my $hash = %(
    wallet   => 100,
    gave     =>   0,
    received =>   0,
    );

for ^1 { $hash<wallet gave> = $hash<wallet gave> Z+ <-1 1> }

dd $hash;

再次获得正确的输出:

Hash $hash = ${:gave(1), :received(0), :wallet(99)}

推荐答案

这是一个错误.自Rakudo 2018.02.1-45-g8a10fc1

It's a bug. Fixed as of Rakudo 2018.02.1-45-g8a10fc1

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