Re: Constructing Context

It turns out that an array in scalar context returns something quite useful -- it's length, or it's content joined with the punctuation variable $,, depending if it is being used as a number or as a string. This is what lets if (!@a) {print "\@a is empty!"} work.

No. You said the two cases are numeric @a and string @a. That's actually @a interpolated and scalar @a. You might even call interpolated-@a as an single-case only type of context except that if you or I did it we'd be wrong. Its also scalar context , it just creates a different optree.

Comment on Re: Constructing Context

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Re: Re: Constructing Context by theorbtwo (Prior) on Dec 17, 2003 at 04:41 UTC
You're right, I was wrong. It turns out that `"@foo"` is not best considered context at all, or, at best, it's a special sort of context that only matters here. When an array is used in scalar context, it returns it's length. Period. However, when an array is interpolated into a string, it magicaly does not get evaluated in scalar context, then inserted into the string. Instead, it's magicly equivlent to `join($", @foo)`. Indeed, the internal operation tree generated by perl for `"@foo"` looks almost exactly like that for `join($", @foo)`, the difference being a "stringify" operation, which seems to mostly shuffle things around a little. Much thanks to diotalevi for pointing this out, pointing me at `-MO=Concise`'s take on what's happening, and for his other critisims on the node. Update: $", not $,, thanks again, demerphq. Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).	[reply] [d/l] [select]

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Re: Re: Constructing Context
by theorbtwo (Prior) on Dec 17, 2003 at 04:41 UTC

You're right, I was wrong. It turns out that "@foo" is not best considered context at all, or, at best, it's a special sort of context that only matters here. When an array is used in scalar context, it returns it's length. Period. However, when an array is interpolated into a string, it magicaly does not get evaluated in scalar context, then inserted into the string.

Instead, it's magicly equivlent to join($", @foo). Indeed, the internal operation tree generated by perl for "@foo" looks almost exactly like that for join($", @foo), the difference being a "stringify" operation, which seems to mostly shuffle things around a little.

Much thanks to diotalevi for pointing this out, pointing me at -MO=Concise's take on what's happening, and for his other critisims on the node.

Update: $", not $,, thanks again, demerphq.

Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).

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