第六章 子过程 和子过程引用

<pre name="code" class="python">第六章   子过程:

   象其他的语言一样,Perl也支持自定义的子程序。（注: 我们也把它们叫做函数,不过,函数和子程序在Perl里是一样的东西。

有时候我们甚至叫它们方法.

@_ 存储的是数组参数
@_  $_[0] 和$_[1]

[oracle@jhoa 20150319]$ cat a3.pl 
sub max {
$max = shift(@_);
for my $item (@_) {
$max = $item if $max < $item;
}
return $max;
}
$bestday = max(20, 8, 12, 16, 30);
print "$bestday is $bestday 
";

[oracle@jhoa 20150319]$ perl a3.pl 
$bestday is 30 

2.3 范围问题:

&foo(1,2,3) # 传递三个参数
foo(1,2,3) # 和上面一样
foo(); # 传递一个空列表
&foo(); # 和上面一样
&foo; # foo() 获取当前的参数，和 foo(@_) 一样，但更快！
foo; # 如果预定义了子过程 foo，那么和 foo() 一样，否则
# 就是光字 "foo"


[oracle@jhoa 20150319]$ cat a4.pl 
sub max {
print "this is test
";
};

$subref =  max;
print "$subref  is $subref 
";

[oracle@jhoa 20150319]$ perl a4.pl 
this is test
$subref  is 1 

获取函数返回值:

间接调用子过程(通过名字或引用)，可以使用下面的任何一种方法：

1. &$subref(LIST) # 在间接调用的时候，& 不能忽略

2. $subref->(LIST) # （除非使用中缀表示法）

3. &$subref # 把当前的 @_ 输出到该子过程


$subref = &name 来获取一个命名子过程的
引用的时候

[oracle@jhoa 20150319]$ cat a4.pl 
sub max {
print "this is test
";
};

$subref =  max;
print "$subref  is $subref 
";
$ref = &max;
print "$ref is $ref
";

[oracle@jhoa 20150319]$ perl a4.pl 
this is test
$subref  is 1 
$ref is CODE(0x1def7080)

&max 函数的引用:

[oracle@jhoa 20150319]$ cat a4.pl 
sub max {
print "this is test
";
};

$subref =  max;
print "$subref  is $subref 
";
$ref = &max;
print "$ref is $ref
";
print "1-------
";
&$ref();

[oracle@jhoa 20150319]$ perl a4.pl 
this is test
$subref  is 1 
$ref is CODE(0x1e73e080)
1-------
this is test


&$ref(); ---调用函数的引用


$subref = &name 来获取一个命名子过程的引用的时候


3.0 传入引用:
[oracle@jhoa 20150319]$ cat t3.pl 
@a=qw/1 2 3 4 5 6 7/;
sub sum {
       my $aref = shift @_;
      foreach (@{$aref}) { $total += $_};
      return  $total;
};

$var = sum (@a);
print "$var is $var
";
[oracle@jhoa 20150319]$ perl t3.pl 
$var is 28


$subref = ∑ 子程序的引用:

&{$subref} 和 $subref->()


[oracle@jhoa 20150319]$ cat t3.pl 
@a=qw/1 2 3 4 5 6 7/;
sub sum {
       my $aref = shift @_;
      foreach (@{$aref}) { $total += $_};
      return  $total;
};
$subref = ∑
print "$subref is $subref
";
$var = &{$subref}(@a);
print "$var is $var
";
[oracle@jhoa 20150319]$ perl t3.pl 
$subref is CODE(0xc2fbe90)
$var is 28

----------------------------------------
[oracle@jhoa 20150319]$ cat t3.pl 
@a=qw/1 2 3 4 5 6 7/;
sub sum {
       my $aref = shift @_;
      foreach (@{$aref}) { $total += $_};
      return  $total;
};
$subref = ∑
print "$subref is $subref
";
$var = &$subref(@a);
print "$var is $var
";
[oracle@jhoa 20150319]$ perl t3.pl 
$subref is CODE(0xa623e90)
$var is 28




&{$subref}    调用子程序的引用

[oracle@jhoa 20150319]$ cat t3.pl 
@a=qw/1 2 3 4 5 6 7/;
sub sum {
       my $aref = shift @_;
      foreach (@{$aref}) { $total += $_};
      return  $total;
};
$subref =  &sum
print "$subref is $subref
";

$a=$subref->(@a);
print "$a is $a
";
[oracle@jhoa 20150319]$ perl t3.pl 
$subref is CODE(0xb833e90)
$a is 28

#################################################
子程序声明:

4.1 内联常量函数