Beefy Boxes and Bandwidth Generously Provided by pair Networks
Welcome to the Monastery
 
PerlMonks  

Re^3: Why/how are these different?

by Athanasius (Monsignor)
on Jan 31, 2013 at 06:46 UTC ( #1016231=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Why/how are these different?
in thread Why/how are these different?

How perverse! Too bad they didn't limit it to 'foreach' and created the confusion.

From the Camel Book (4th Edition, 2012, page 142):

For historical reasons, the foreach keyword is a synonym for the for keyword, so you can use for and foreach interchangeably, whichever you think is more readable in a given situation. We tend to prefer for because we are lazy and because it is more readable, especially with the my. (Don’t worry—Perl can easily distinguish for (@ARGV) from for ($i=0; $i<$#ARGV; $i++) because the latter contains semicolons.)
And to think I stayed away from 'foreach' specifically because many books recommend doing so because it uses more memory (and I'm working with large arrays)...

I could be wrong, but I think this advice is outdated (if it was ever correct). Again from the Camel Book (page 143):

If LIST consists of assignable values (meaning variables, generally, not enumerated constants), you can modify each of those variables by modifying VAR inside the loop. That’s because the loop variable becomes an implicit alias for each item in the list that you’re looping over.

If I’m reading that correctly, no copying is needed, so there’s no reason a foreach-style loop would use more memory than a C-style for loop.

And there are significant benefits. See Foreach Loops in perlsyn, where a C-style for loop is rewritten as a foreach-style loop in idiomatic Perl, and the latter is stated to be “cleaner, safer, and faster.” And the Camel Book has this in its cosideration of “Time Efficiency” (pages 691–2):

Avoid subscripting when a foreach or list operator will do.... There’s often a better way to do it. Consider using foreach, shift, and splice operations.

Hope that helps,

Athanasius <°(((><contra mundum Iustus alius egestas vitae, eros Piratica,


Comment on Re^3: Why/how are these different?
Select or Download Code
Re^4: Why/how are these different?
by perl-diddler (Hermit) on Jan 31, 2013 at 19:41 UTC
    Ok, I gotta love this part:

    <quote> For historical reasons, the foreach keyword is a synonym for the for keyword, so you can use for and foreach interchangeably, whichever you think is more readable in a given situation. We tend to prefer for because we are lazy and because it is more readable, especially with the my. </quote>

    1) For historical reasons we regard the world as flat. It remains so for compatibility purposes! *ahem*.

    <quote> (Don’t worry—Perl can easily distinguish for (@ARGV) from for ($i=0; $i<$#ARGV; $i++) because the latter contains semicolons.) </quote>

    2) Eh? Now this sounds like a bug .. implementation not following design. Mine DID contain semicolons which were ignored and cast off as warnings or errors (w/parens). That seems a case of implementation not following intent of design, no?

    p.s.- for compatibility reasons <quote> is not? supported?

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1016231]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others chanting in the Monastery: (6)
As of 2014-08-02 10:03 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    Who would be the most fun to work for?















    Results (55 votes), past polls