这肯定是非常简单的问题,但我仍在学习,没有找到答案。
需要检查提供给 Moose 对象构造函数的(必需)参数的有效性,例如,如下例所示:
use 5.016;
use warnings;
package My {
use Moose;
has 'mydir' => (
is => 'ro',
isa => 'Str',
required => 1,
);
}
use File::Path qw(remove_tree);
package main {
my @dirs = qw(./d1 ./d2);
#ensure no one dir exists
remove_tree($_) for ( @dirs );
#create the first dir
mkdir $dirs[0] or die;
foreach my $dir( @dirs ) {
my $m = My->new( mydir=>$dir );
say "$dir ", defined($m) ? "" : "NOT", " ok";
}
}
问题是:我应该向My
包中添加什么以确保仅在提供的mydir
路径存在时才创建My
对象?所以某处需要添加测试if -d ...
.
如何定义属性mydir
有效性检查?
主程序的通缉结果:
./d1 ok
./d2 NOT ok
可以使用类型约束定义子类型。
用于处理此功能的语法糖由 Moose::Util::TypeConstraints 提供。
package My;
use 5.16.0;
use Moose;
use Moose::Util::TypeConstraints; # provides sugar below
subtype 'ExistingDir' => (
as 'Str',
where { -d $_ },
message { 'The directory does not exist' }
);
has 'mydir' => (
is => 'ro',
isa => 'ExistingDir',
required => 1,
);
package main;
my $foo = My->new(mydir => 'perl'); # exists
say $foo->mydir();
my $bar = My->new(mydir => 'perlXXX'); # does not exist, so dies here...
输出:
>mkdir perl
>perl foo.pl
perl
Attribute (mydir) does not pass the type constraint because: The directory does not exist at ...