我为类定义了AT-POS
方法并导出了[]
运算符。但是,当我在该类的实例上使用[]
时,编译器忽略了我定义的运算符。
这是代码:
unit module somelib;
class SomeClass is export {
method AT-POS(@indices) {
say "indices are {@indices.perl}"
}
}
multi postcircumfix:<[ ]> (SomeClass:D $inst, *@indices) is export {
$inst.AT-POS(@indices)
}
#! /usr/bin/env perl6
use v6.c
use lib ".";
use somelib;
my $inst = SomeClass.new;
$inst[3, 'hi'];
# expected output:
# indices are 3, 'hi'
# actual output:
# Type check failed in binding to parameter '@indices';
# expected Positional but got Int (3)
# in method AT-POS at xxx/somelib.pm6 (somelib) line 4
# in block <unit> at ./client.pl6 line 8
那么这段代码有什么问题呢?
更新:
我确实需要将多个索引传递给AT-POS方法我很惊讶地发现当我修正错字时使用* $ indices而不是* @ indices给出了预期的输出。我不知道存在像* $ some-parameter这样的用法。它有效还是只是编译器的错误?
unit module somelib;
class SomeClass is export {
method AT-POS($indices) {
say "indices are {$indices.perl}"
}
}
multi postcircumfix:<[ ]> (SomeClass:D $inst, *$indices) is export {
$inst.AT-POS($indices)
}
#! /usr/bin/env perl6
use v6.c;
use lib ".";
use somelib;
my $inst = SomeClass.new;
$inst[3, 'hi'];
# expected output:
# indices are 3, 'hi' # or something like it
# actual output:
# indices are $(3, "hi") # It's ok for me.
问题是AT-POS
只能获得一维Positional
的单个参数。如果指定切片,则该设置将负责多次调用AT-POS
并将结果收集到列表中:
class A {
method AT-POS($a) { 2 * $a }
}
dd A.new[1,2,3,4]; # (2,4,6,8)
此外,你不需要提供postcircumfix:<[ ]>
候选人,除非你真的想做非常特殊的事情:提供的设置将自动发送到正确的AT-POS
。