What does &@ mean for sub?

Question

Possible Duplicate:
What does the function declaration “sub function($$)” mean?

sub t(&@) {
    print @_;
}
t {print 1};

I tried to change &@ to &$ and it will fail.

What's the lingo for it so that I can search?

See line 8 in the code example [here](http://perldoc.perl.org/perlsub.html#Prototypes) — Ray Toal, Sep 21 '11 at 05:24
Also see [this old rant](http://www.perlmonks.org/?node_id=406231) about why you probably shouldn't use prototypes anyway. — Grant McLean, Sep 21 '11 at 23:04

Alan Haggai Alavi · Accepted Answer · 2011-09-21T05:38:17.050

5

&@ is a subroutine prototype. This lets you create syntax similar to the builtin grep function (accepts a BLOCK and then a LIST). The LIST can even be the empty list: ().

&$ when used will force the second argument (which is mandatory) to be evaluated in scalar context. Since there is no second argument in t {print 1}; it will fail to compile.

Read more about subroutine prototypes at: perldoc perlsub.

edited Sep 21 '11 at 05:38

answered Sep 21 '11 at 05:25

Alan Haggai Alavi

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What's the difference between `&$` and `&;$`? – new_perl Sep 21 '11 at 05:51
The `;` makes the rest of the arguments optional. – Alan Haggai Alavi Sep 21 '11 at 05:54

cftarnas · Answer 2 · 2011-09-21T05:50:26.460

1

I'm not quite clear on what you want the code to do, but you are creating a prototype for your sub, see the perldocs. The & means the sub t takes a block as the first argument and the @ means the rest of the arguments are an array.

When you call your function, you are passing it one argument, the block {print 1} and that is what you are then printing out - the CODE reference as a string. The reason &$ fails is you are not passing a second argument. That is fine for &@ as the second argument is the empty array.

edited Sep 21 '11 at 05:50

answered Sep 21 '11 at 05:26

cftarnas

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Whats with the drive-by downvotes for all of the answers? – cftarnas Sep 21 '11 at 05:48
Someone is working against the community, I reckon. – Alan Haggai Alavi Sep 21 '11 at 05:57

score 0 · Answer 3 · answered Sep 21 '11 at 05:25

0

The term you are looking for is "perl function prototypes".

answered Sep 21 '11 at 05:25

Hugh

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score 0 · Answer 4 · answered Sep 21 '11 at 05:25

0

"Function prototype", http://perldoc.perl.org/perlsub.html#Prototypes

answered Sep 21 '11 at 05:25

tripleee

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What does &@ mean for sub?

4 Answers4