作者liyih ()
看板Perl
标题Re: [问题] 串列问题
时间Mon Mar 14 14:23:23 2011
※ 引述《StarTouching (抚星)》之铭言：
: 我是Perl新手 有程式基础 对串列有个小问题....
: 串列给定可以这样写:
: @ary = (1,2,3);
: 或
: @ary = (1..10);
: 或
: @ary = @seq;
: 而foreach这样用:
: foreach(1,2,3){}
: 或
: foreach(1..10){}
: 或
: foreach(@seq){}
: 这样有个小问题是 (1,2,3)才能代表串列 那为什麽foreach没有两层括弧?
: 如果串列的括弧可以被省略 那为什麽 @ary = 1,2,3; 这样不行?
: 我知道Perl是个方便为上的语言,
: 但为求方便记忆, 想说还是问问看。
: 请问我该怎麽理解呢?
# perldoc perlsyn
Statement Modifiers
...略...
if EXPR
unless EXPR
while EXPR
until EXPR
foreach LIST
^^^^
...略...
The "foreach" modifier is an iterator: it executes the statement once
for each item in the LIST (with $_ aliased to each item in turn).
print "Hello $_!\n" foreach qw(world Dolly nurse);
# perldoc perlop
1. Comma Operator 「,」
...略...
In list context, it’s just the list argument separator, and inserts
^^^^^^^^^^^^^^^^^^^^^^^
both its arguments into the list. These arguments are also evaluated
from left to right.
...略...
2. Terms and List Operators
...略...
A TERM has the highest precedence in Perl. They include variables,
quote and quote-like operators, any expression in parentheses, and any
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
function whose arguments are parenthesized. Actually, there aren’t
^^^^^^^^^^^^^ ^^^^^^^^^^^^^
really functions in this sense, just list operators and unary operators
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
behaving as functions because you put parentheses around the arguments.
These are all documented in perlfunc.
...略...
3. Range Operators 「..」
Binary ".." is the range operator, which is really two different
operators depending on the context. In list context, it returns a list
of values counting (up by ones) from the left value to the right value.
...略...
大致上摘录 perldoc 的内容，应该可以发现其中的差异。
--
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◆ From: 140.114.64.130
1F：推 StarTouching:所以 1,2,3 跟 1..2 不足以代表串列罗? 03/15 23:29
2F：→ StarTouching:foreach LIST, 那为何 foreach @ary 这样写不行? 03/15 23:29
3F：推 rkcity:@ary=(1,2,3); print foreach @ary; 03/17 18:37