What means "class" here?

honoluludesktop · 31 Jan 2011, 19:07

What's the difference if any?

ss = model.selection
ss.each do |e|
  if e.class == Sketchup;;ComponentInstance
    #other stuff
  end
end

ss = model.selection
ss.each do |e|
  if e.is_a? Sketchup;;ComponentInstance
    #other stuff
  ebd
end

tt, or anyone else, how do I get color in my code? "Font colour" doesn't seem to do it.

thomthom · 31 Jan 2011, 19:16

is_a? checks for inheritance as well.

<span class="syntaxdefault"><br />class Foo<br />end<br /><br />class Bar </span><span class="syntaxkeyword"><</span><span class="syntaxdefault"> Foo<br />end<br /><br />f </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> Foo</span><span class="syntaxkeyword">.new<br /></span><span class="syntaxdefault">b </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> Bar</span><span class="syntaxkeyword">.new<br /><br /></span><span class="syntaxdefault">f</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">class </span><span class="syntaxkeyword">==</span><span class="syntaxdefault"> Foo </span><span class="syntaxcomment"># => true<br /></span><span class="syntaxdefault">b</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">class </span><span class="syntaxkeyword">==</span><span class="syntaxdefault"> Foo </span><span class="syntaxcomment"># => false<br /></span><span class="syntaxdefault">b</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">class </span><span class="syntaxkeyword">==</span><span class="syntaxdefault"> Bar </span><span class="syntaxcomment"># => true<br /><br /></span><span class="syntaxdefault">f</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">is_a</span><span class="syntaxkeyword">?(</span><span class="syntaxdefault">Foo</span><span class="syntaxkeyword">)</span><span class="syntaxdefault"> </span><span class="syntaxcomment"># => true<br /></span><span class="syntaxdefault">b</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">is_a</span><span class="syntaxkeyword">?(</span><span class="syntaxdefault">Foo</span><span class="syntaxkeyword">)</span><span class="syntaxdefault"> </span><span class="syntaxcomment"># => true<br /></span><span class="syntaxdefault">b</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">is_a</span><span class="syntaxkeyword">?(</span><span class="syntaxdefault">Bar</span><span class="syntaxkeyword">)</span><span class="syntaxdefault"> </span><span class="syntaxcomment"># => true<br /></span><span class="syntaxdefault"> </span>

honoluludesktop · 31 Jan 2011, 19:47

Had to look up "inheritance" to get it. Thanks.

Dan Rathbun · 1 Feb 2011, 11:36

@hd said:

tt, or anyone else, how do I get color in my code?

We are cheating, the color lexer for php is built-in to phpBB, so we are change the 1st code tag:

It does not properly color Ruby but ... we are impatient.

[code=php]

thomthom · 1 Feb 2011, 13:07

@dan rathbun said:

This is a wee bit slower because on the C side:[list]

Results seems negligible though: http://forums.sketchucation.com/viewtopic.php?f=323&t=19576&st=0&sk=t&sd=a&start=15#p166698
The difference between the test of the same method differs just as must as the difference between .is_a? and .class.
Maybe performance is more noticeable if the objects has higher levels of inheritance, but there seem to be no practical savings in .class ==

Dan Rathbun · 1 Feb 2011, 13:41

@thomthom said:

Results seems negligible though: http://forums.sketchucation.com/viewtopic.php?f=323&t=19576&st=0&sk=t&sd=a&start=15#p166698

Well ... compiled C is really fast!! We are talking about milliseconds here.

Nice .. but. How many times did you run the tests ?
I've found it really takes a minimum of 8 times (saving the results, then taking the mean of the total.)

@thomthom said:

The difference between the test of the same method differs just as must as the difference between .is_a? and .class.

I don't see that in the numbers.. I see that using the alias .is_a? takes a wee bit more time that calling .kind_of? directly.

@thomthom said:

Maybe performance is more noticeable if the objects has higher levels of inheritance, but there seem to be no practical savings in .class ==

I would agree with 'higher levels' as the C while loop must eat time...

The main reason I do it (and encourage it,) is for readability. If your testing for class equality, I use the == it's only 2 more characters (as .class and .is_a? both have the same number of characters.)

BUT.. your reply just made me realize something I missed.
object.class==ClassName is actually calling 2 Ruby methods, whereas:
object.kind_of? ClassName is only calling 1 Ruby method, so ....
in long loops, kind_of?() is bound to be faster(the fastest of the three.)

Dan Rathbun · 1 Feb 2011, 13:53

@honoluludesktop said:

What's the difference if any?

.is_a?() is a bit misleading, it is an alias for .kind_of?() (which I prefer to use instead.)

if e.class == Sketchup::ComponentInstance

This is faster than .is_a?() or kind_of?() because:
EDIT: not so.. I forgot that both .class() AND .==() are both method calls, and kind_of?() is only one call so it's faster. (see posts further down.)

class Class inherits it's ==() method from class Object, via class Module. The Object.==() method, is implemented in C, as a simple if statement:

static VALUE
rb_obj_equal(obj1, obj2)
    VALUE obj1, obj2;
{
    if (obj1 == obj2) return Qtrue;
    return Qfalse;
}

if e.is_a? Sketchup::ComponentInstance

This is a wee bit slower because on the C side:

it has to go through a switch statement for typechecking, then through a while loop

VALUE
rb_obj_is_kind_of(obj, c)
    VALUE obj, c;
{
    VALUE cl = CLASS_OF(obj);

    switch (TYPE(c)) {
      case T_MODULE;
      case T_CLASS;
      case T_ICLASS;
        break;

      default;
        rb_raise(rb_eTypeError, "class or module required");
    }

    while (cl) {
        if (cl == c || RCLASS(cl)->m_tbl == RCLASS(c)->m_tbl)
            return Qtrue;
        cl = RCLASS(cl)->super;
    }
    return Qfalse;
}

Since all Sketchup's Drawingelement subclasses have NO subclasses of their own, using .is_a?() or .kind_of?() is pointless, IF the argument is the Drawingelement subclass your testing for.

So when should you use .is_a?() or .kind_of?() ??
EDIT: Always when iterating, especially the model or other large collections, use kind_of? or is_a? (see posts further down.)

When iterating the objects in a model, if you are only interested in those "kind of" objects that are drawing elements, and you wish to ignore such objects as layers, views, pages, shadowinfo, etc.; then you would use:
if e.kind_of?( Sketchup::Drawingelement )
which returns true only for objetcs like faces, edges, curves, etc.

thomthom · 1 Feb 2011, 13:58

@dan rathbun said:

Nice .. but. How many times did you run the tests ?

I ran them on models I had, you see the model status under the data results.

@dan rathbun said:

I don't see that in the numbers.. I see that using the alias .is_a? takes a wee bit more time that calling .kind_of? directly.

First test:
` is_a? - 0.89c
kind_of? - 0.782c

class - 0.875c`

Second test:
` is_a? - 16.297c
kind_of? - 16.141c

class - 18.703c`

The odd bit is the .class call being slower in the second test. I credit the difference to other system variations.
Since is_a? and kind_of? are aliases they should be the same. (If we tested spherical chickens in vacuum. )

@dan rathbun said:

I've found it really takes a minimum of 8 times (saving the results, then taking the mean of the total.)

Yea - I didn't do that.

Dan Rathbun · 1 Feb 2011, 14:03

@thomthom said:

The odd bit is the .class call being slower in the second test. I credit the difference to other system variations.

Nope ... not variables.

Its actually *object*.class().==( *argument* )

@dan rathbun said:

BUT.. your reply just made me realize something I missed.

object.class==ClassName is actually calling 2 Ruby methods, whereas:
object.kind_of? ClassName is only calling 1 Ruby method,
so ....
in long loops, kind_of?() is bound to be faster(the fastest of the three.)

thomthom · 1 Feb 2011, 14:19

That's a good point. I still keep forgetting that == as method .==.

david. · 1 Feb 2011, 18:02

Don't forget instance_of? when only looking for a specific class without regard to inheritance. As in

<span class="syntaxdefault"><br />ss </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> model</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">selection<br />ss</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each do </span><span class="syntaxkeyword">|</span><span class="syntaxdefault">e</span><span class="syntaxkeyword">|<br /></span><span class="syntaxdefault">  if e</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">instance_of</span><span class="syntaxkeyword">?</span><span class="syntaxdefault"> Sketchup</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">ComponentInstance<br />    </span><span class="syntaxcomment">#other stuff<br /></span><span class="syntaxdefault">  end<br />end</span>