Optimization Tips

[AdamB]

OT: Any chance the forum administrator of SCF can fix the [ruby] tag to not remove formatting. Formatting is a big part of understanding code, and while for regular text collapsing whitespace down to a single space might work, for code it does not.

[thomthom]

OT: Any chance the forum administrator of SCF can fix the tag to not remove formatting. Formatting is a big part of understanding code, and while for regular text collapsing whitespace down to a single space might work, for code it does not.

I think the [ruby]ruby is meant for inline code. While you got the code tag for block codes. (Though I wish there was a way to expand it - I loathe internal scrollbars.)

[thomthom]

Interesting test Adam:

doit
6.474
3.292
nil

Note: I increased the number of iterations (10000000.times { ... })

[thomthom]

Didn't realise Ruby would recreate the variables for each iteration. I'd thought it'd keep them for the duration of the loop...

[AdamB]

Seems an arbitrary (and wrong) assumption that inline code requires removing whitespace. Why not just leave in what the author wrote rather than trying to second guess? Whatever.

[thomthom]

Agree - whitespace eating of ruby has bothered me as well. Will ask if it can be changed.

[AdamB]

Didn't realise Ruby would recreate the variables for each iteration. I'd thought it'd keep them for the duration of the loop...

The closure you create with curly braces is handled as a first class object and passed as an argument to the iterator. This means the scope of any variables you mention inside that block is limited to that block - it must create them each time.

[thomthom]

Is that why each is slow?

[Gaieus]

Guys, Thom asked if we can do something with these white spaces but I have to say it is most probable that we cannot. I is hard coded somewhere in the php script of the forum software and even if we could tweak that, it would be impossible to keep it through upgrades (which is very due soon anyway).

Is the code tag not good (apart from that scrolling annoyance)?

[thomthom]

It's ok. I just hoped there was a config UI for BBCode tags on the forum. Thought it was normal. The code tag is ok, just figured if it could be changed...

I don't suppose there are forum plugins that can be installed? having the code block apply syntax highlighting would be a delight for us coders. Such as this:

http://code.google.com/p/syntaxhighlighter/

Edit: what version of phpBB does SCF run? I'm looking at this: http://www.phpbb.com/kb/article/adding- ... in-phpbb3/ from this it appear to be that it'd be a matter of setting the HTML replacement for the ruby tag to not collapse white space using CSS.

Replacement sample something like this:
<span style="white-space:pre;">{TEXT}</span>

[Gaieus]

I can imagine you would like that syntax highlight! I use Notepad++ and know what a difference it is!

Coen and Tavi should be spoken to about these things.

[thomthom]

I see a lot of SU scripts using some of the more compact iterators Ruby iterators. So they might read nice, but they're often slower than just simple for-loops.

http://blog.shingara.fr/each-vs-for.html

In regard to this should one init the variables used by for in to speed up things? or is that not needed?

Would this
x = 0
for x in collection
# ...
end
be faster than
for x in collection
# ...
end

[AdamB]

no

[Jim]

I've always thought for used each under the hood.

http://blog.grayproductions.net/article ... e_for_loop

for loops do not have their own scope - the loop variable and any variables created in the loop become available (or are over-written) in the current scope.

With .each, variables are local to the block {..}

[thomthom]

I've always thought for used each under the hood.

http://blog.grayproductions.net/article ... e_for_loop

for loops do not have their own scope - the loop variable and any variables created in the loop become available (or are over-written) in the current scope.

If you click the method names in the Ruby API manual you get to see the sourcecode:
http://ruby-doc.org/core/classes/Array.html#M002173

[Jim]

That's showing a for loop in the c language.

[thomthom]

That's what it's doing under the hood.

[Jim]

That's what it's doing under the hood.

Right, so where is the definition for the for function?

The answer is there isn't one because for is not a function, but is "sugar". The for loop in Ruby really uses the .each method behind the scenes.

Although, I can't recall where I learned that. The link to the blog article mentions it, though.

[tbd]

speaking of each vs for :

Code: Select all

loop1 = []
loop2 = []

calls = ["one", "two", "three"]

calls.each do |c|
  loop1 << Proc.new { puts c }
end

for c in calls
  loop2 << Proc.new { puts c }
end

loop1[1].call #=> "two"
loop2[1].call #=> "three"

[Dan Rathbun]

The for loop in Ruby really uses the .each method behind the scenes. ... Although, I can't recall where I learned that.

'Pick-Axe' > For ... In expressions

[Jim]

I guess to get back on topic, for loops are not faster then .each iterators. The performance must have to do with how the for loop variables are not loop scoped, as in each.

[thomthom]

Came across this link:
http://www.h3rald.com/articles/efficien ... ut-review/

On that list it says

Use parallel assignment (a, b = 5, 6) where applicable

while at this link:
http://www.hxa.name/articles/content/ru ... _2007.html

Avoid parallel assignment

[thomthom]

Came across this link:
http://www.h3rald.com/articles/efficien ... ut-review/

On that list it says

Use parallel assignment (a, b = 5, 6) where applicable

while at this link:
http://www.hxa.name/articles/content/ru ... _2007.html

Avoid parallel assignment

I just bought the ebook and that review summary was wrong - parallel assignments are not recommended for performance important tasks.
Interesting read that book btw.

[MartinRinehart]

Let's see - for performance I'm going to avoid iterations, arrays, hashes and objects.

What's left?

[thomthom]

What's left?

puts "Hello World"

[AdamB]

I guess to get back on topic, for loops are not faster then .each iterators. The performance must have to do with how the for loop variables are not loop scoped, as in each.

"Your racing car is not faster than my Trabant, it just covers more ground in a shorter time than my car."

[cjthompson]

Has anyone looked into Enumerable.grep()? it seems pretty useful, but I don't know how fast it is.

[Jim]

I guess to get back on topic, for loops are not faster then .each iterators. The performance must have to do with how the for loop variables are not loop scoped, as in each.

"Your racing car is not faster than my Trabant, it just covers more ground in a shorter time than my car."

Heh? Oh. Yes, I see.

Would it be correct to say: An each loop can be as fast as a for loop if the loop variable has been initialized?

[thomthom]

That would mean it's not the each loop itself that's slow - but the creation of variables.

[Jim]

Exactly.