Optimization Tips
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@thomthom said:
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.
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Is that why
eachis slow? -
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)?
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It's ok. I just hoped there was a config UI for BBCode tags on the forum. Thought it was normal. The
codetag 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:
Edit: what version of phpBB does SCF run? I'm looking at this: http://www.phpbb.com/kb/article/adding-custom-bbcodes-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> -
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.
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@adamb said:
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.
In regard to this should one init the variables used by
for into speed up things? or is that not needed?Would this
` x = 0
for x in collection...
end
be faster thanfor x in collection...
end`
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no
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I've always thought
forusedeachunder the hood.http://blog.grayproductions.net/articles/the_evils_of_the_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 {..} -
@jim said:
I've always thought
forusedeachunder the hood.http://blog.grayproductions.net/articles/the_evils_of_the_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 -
That's showing a for loop in the c language.
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That's what it's doing under the hood.
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@thomthom said:
That's what it's doing under the hood.
Right, so where is the definition for the
forfunction?The answer is there isn't one because
foris not a function, but is "sugar". Theforloop in Ruby really uses the.eachmethod behind the scenes.Although, I can't recall where I learned that. The link to the blog article mentions it, though.
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speaking of each vs for :
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" -
@jim said:
The
forloop in Ruby really uses the.eachmethod behind the scenes. ... Although, I can't recall where I learned that. -
I guess to get back on topic, for loops are not faster then .each iterators. The performance must have to do with how the
forloop variables are not loop scoped, as ineach. -
Came across this link:
http://www.h3rald.com/articles/efficient-ruby-code-shortcut-review/On that list it says
@unknownuser said:Use parallel assignment (a, b = 5, 6) where applicable
while at this link:
http://www.hxa.name/articles/content/ruby-speed-guide_hxa7241_2007.html@unknownuser said:
Avoid parallel assignment
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@thomthom said:
Came across this link:
http://www.h3rald.com/articles/efficient-ruby-code-shortcut-review/On that list it says
@unknownuser said:Use parallel assignment (a, b = 5, 6) where applicable
while at this link:
http://www.hxa.name/articles/content/ruby-speed-guide_hxa7241_2007.html@unknownuser said:
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. -
Let's see - for performance I'm going to avoid iterations, arrays, hashes and objects.
What's left?
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@jim said:
I guess to get back on topic, for loops are not faster then .each iterators. The performance must have to do with how the
forloop variables are not loop scoped, as ineach."Your racing car is not faster than my Trabant, it just covers more ground in a shorter time than my car."
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