# Understanding ruby? need help

**URL:** <https://www.ruby-forum.com/t/understanding-ruby-need-help/70110>\
**Category:** Ruby\
**Created:** [February 18, 2006, 6:32pm UTC](https://www.ruby-forum.com/t/understanding-ruby-need-help/70110 "2006-02-18T18:32:16Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![bbqbaker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ecccb3/32.png) [@bbqbaker](https://www.ruby-forum.com/u/bbqbaker)\
**Post date:** [February 18, 2006, 6:32pm UTC](https://www.ruby-forum.com/t/understanding-ruby-need-help/70110/1 "2006-02-18T18:32:16Z")

</div>

I hi,  
I am new to ruby and bought my first book. i am having sort of difficult  
time understanding blocks/yeild statements. i am coming from C++.

class Array  
def find  
for i in 0…size  
value = self[i]  
return value if yield(value)  
end  
return nil  
end  
end

[1,3,5,7,9].find {|v| v\*v \> 30}

-\> 7

in the last line of code, it is passing to function find each number one  
by one thats on the left? when it hits the “return value if  
yield(value)” it will pass parameter value to the block and v will now  
be equal to value, and then perform the code v\*v \> 30. if that is true,  
it will get out of fuction find.

so what is in between the |" "| of the block is like in c++:

bool code\_blk(int v)  
{  
if (v \* v \> 30)  
return TRUE;  
else  
return FALSE;  
}

is this kind of right?? thanks

---

<div class="post-metadata">

**Author:** ![bbqbaker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ecccb3/32.png) [@bbqbaker](https://www.ruby-forum.com/u/bbqbaker)\
**Post date:** [February 18, 2006, 10:41pm UTC](https://www.ruby-forum.com/t/understanding-ruby-need-help/70110/2 "2006-02-18T22:41:07Z")

</div>

On Feb 18, 2006, at 12:32 PM, bbqbaker wrote:

> ```
> end
> 
> ```
> 
> in the last line of code, it is passing to function find each  
> bool code\_blk(int v)  
> {  
> if (v \* v \> 30)  
> return TRUE;  
> else  
> return FALSE;  
> }
> 
> is this kind of right?? thanks

Basically yes:

however if I was writing in C++ I’d probably say:

bool code\_blk(int v)  
{  
return v \* v \> 30;  
}

the extra branch is really unecessary

---

<div class="post-metadata">

**Author:** ![bbqbaker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ecccb3/32.png) [@bbqbaker](https://www.ruby-forum.com/u/bbqbaker)\
**Post date:** [February 19, 2006, 11:02am UTC](https://www.ruby-forum.com/t/understanding-ruby-need-help/70110/3 "2006-02-19T11:02:31Z")

</div>

On 2/18/06, bbqbaker [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> is this kind of right?? thanks

Yep, that’s basically it. Coming from C++, I also had a tough time  
with blocks at first (but they are so great, so it’s worth the  
effort).

I wrote a tutorial that talks, among other things, about a somewhat  
different approach to understanding blocks and procs:

[http://pine.fm/LearnToProgram/?Chapter=10](http://pine.fm/LearnToProgram/?Chapter=10)

and, of course, it’s also covered in my book:

[http://www.pragmaticprogrammer.com/titles/fr\_ltp/](http://www.pragmaticprogrammer.com/titles/fr_ltp/)

(The book covers what’s in the tutorial, but considerably more in  
depth, and with the benefit of the feedback I got from the tutorial  
(which came first), as well as covering things that never made it into  
the tutorial.)

Essentially, what I found confusing was “yield”. Once you look at the  
problem from the angle of little functions (like the C++ function you  
wrote) that you pass around explicitly, it makes more sense (to me, at  
least).

Once I wrapped my head around that, it wasn’t hard to see yield and  
the “do |…| code-code-code end” syntax as just shortcuts to make the  
whole process easier to program.

And for the record, I still think “yield” is a weird name for it. 🙂

Chris

---

<div class="post-metadata">

**Author:** ![bbqbaker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ecccb3/32.png) [@bbqbaker](https://www.ruby-forum.com/u/bbqbaker)\
**Post date:** [February 19, 2006, 11:38am UTC](https://www.ruby-forum.com/t/understanding-ruby-need-help/70110/4 "2006-02-19T11:38:54Z")

</div>

Chris P. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> On 2/18/06, bbqbaker [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > is this kind of right?? thanks
> 
> Yep, that’s basically it. Coming from C++, I also had a tough time  
> with blocks at first (but they are so great, so it’s worth the  
> effort).

C++ might want to compare blocks with functors. I like to think of them  
as  
anonymous functions with a closure. Often the closure is’t even needed,  
such in simple examples where the block only operates on its arguments.

> I wrote a tutorial that talks, among other things, about a somewhat  
> different approach to understanding blocks and procs:
> 
> [http://pine.fm/LearnToProgram/?Chapter=10](http://pine.fm/LearnToProgram/?Chapter=10)

Chris, I can’t see “yield” mentioned on that page. Is it just me, did I  
overlook it? Is this intentionally? I mean, “yield” would be the first  
thing that I’d describe on such a page; IMHO it’s the default way to go  
when  
passing blocks to methods (it’s also the fastest AFAIK). I only use  
&block  
if I have to store the block in a variable and / or have to pass it on  
to  
another (recursive) method call.

> problem from the angle of little functions (like the C++ function you  
> wrote) that you pass around explicitly, it makes more sense (to me, at  
> least).
> 
> Once I wrapped my head around that, it wasn’t hard to see yield and  
> the “do |…| code-code-code end” syntax as just shortcuts to make the  
> whole process easier to program.

If you look at the block as anonymous function it’s clear that one needs  
a  
special syntax to invoke it (can’t use the name). That’s exactly what  
“yield” does.

> And for the record, I still think “yield” is a weird name for it. 🙂

OTOH this has the advantage of drawing people’s attention to it which  
probably makes reading code easier. 🙂

Kind regards

```
robert

```

---

<div class="post-metadata">

**Author:** ![bbqbaker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ecccb3/32.png) [@bbqbaker](https://www.ruby-forum.com/u/bbqbaker)\
**Post date:** [February 22, 2006, 4:19pm UTC](https://www.ruby-forum.com/t/understanding-ruby-need-help/70110/5 "2006-02-22T16:19:26Z")

</div>

> > I wrote a tutorial that talks, among other things, about a somewhat  
> > different approach to understanding blocks and procs:
> > 
> > [http://pine.fm/LearnToProgram/?Chapter=10](http://pine.fm/LearnToProgram/?Chapter=10)
> 
> Chris, I can’t see “yield” mentioned on that page. Is it just me, did I  
> overlook it? Is this intentionally?

Yep. On the next page (Chapter=11), I talk about, among other things,  
yield. But I wanted to bring it in later as another way of doing it.

> I mean, “yield” would be the first  
> thing that I’d describe on such a page; IMHO it’s the default way to go when  
> passing blocks to methods (it’s also the fastest AFAIK).

Default way to go for an experienced programmer to use? Or for a  
non-programmer to learn? Very different situations. 🙂

> I only use &block  
> if I have to store the block in a variable and / or have to pass it on to  
> another (recursive) method call.

Me, too… unless I’m teaching someone about it, because “yield” just  
throws people off in my experience (not just my personal experience,  
but my experience in teaching others).

> If you look at the block as anonymous function it’s clear that one needs a  
> special syntax to invoke it (can’t use the name). That’s exactly what  
> “yield” does.

Well, there’s “anonymous” (like &block), and then there’s _invisible_,  
like what yield is calling. There’s a big difference. I’m just  
trying to make it visible, which is an important step on the way to  
understandable.

Plus, passing a function around, and calling a function… these  
things are extensions of what the reader has already learned at that  
point. “yield” is something totally new. Better to describe this in  
terms of something the reader is more familiar with first; then I can  
just say “yield is a magical shortcut”. Because it sort of it, right?  
It’s magical, and magical is (among other things) weird. That’s my  
hypothesis, anyway. 🙂

Yield: it’s something you do to traffic with the right of way. It’s  
how many cookies your recipe is “supposed” to make if you don’t eat  
any of the dough. I can see the (imho, weak) analogy to  
programming… but I think that describing what is going on in as  
plain of terms as possible is the best way to teach this.

In any case, the PickAxe does it the other way, so hopefully we have  
every learning style covered. 🙂

Chris

---

<div class="post-metadata">

**Author:** ![bbqbaker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/ecccb3/32.png) [@bbqbaker](https://www.ruby-forum.com/u/bbqbaker)\
**Post date:** [February 24, 2006, 5:39pm UTC](https://www.ruby-forum.com/t/understanding-ruby-need-help/70110/6 "2006-02-24T17:39:23Z")

</div>

Sorry for the late reply. Apparently your posting didn’t make it to  
the news group (yet). I start getting really annoyed by this half  
working gateway.

2006/2/22, Chris P. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> > > I wrote a tutorial that talks, among other things, about a somewhat  
> > > different approach to understanding blocks and procs:
> > > 
> > > [http://pine.fm/LearnToProgram/?Chapter=10](http://pine.fm/LearnToProgram/?Chapter=10)
> > 
> > Chris, I can’t see “yield” mentioned on that page. Is it just me, did I  
> > overlook it? Is this intentionally?
> 
> Yep. On the next page (Chapter=11), I talk about, among other things,  
> yield. But I wanted to bring it in later as another way of doing it.

Ah, I see.

> > I mean, “yield” would be the first  
> > thing that I’d describe on such a page; IMHO it’s the default way to go when  
> > passing blocks to methods (it’s also the fastest AFAIK).
> 
> Default way to go for an experienced programmer to use? Or for a  
> non-programmer to learn? Very different situations. 🙂

I can only speak from my experience: I learned yield earlier and the  
only thing I found difficult about it that I couldn’t figure how to  
pass a block on to some other method. I knew there had to be a way but  
the manual forwarding with a block seemed to awkward… 🙂

> things are extensions of what the reader has already learned at that  
> point. “yield” is something totally new. Better to describe this in  
> terms of something the reader is more familiar with first; then I can  
> just say “yield is a magical shortcut”. Because it sort of it, right?  
> It’s magical, and magical is (among other things) weird. That’s my  
> hypothesis, anyway. 🙂

Sounds quite reasonable. I never looked at it this way - and never  
experienced similar problems (probably because I never gave a Ruby  
class :-)).

The way I’d do it is explain if you have a method that accepts a block  
use yield to invoke it. Yield is like a function call, arguments are  
passed on to the block and the block’s return value is returned from  
yield. Oh, and btw. if you want to store that block, pass it on to  
another method or change it’s scope with instance\_eval you can access  
it directly by adding &block at the end of the method’s argument list  
like this:

> In any case, the PickAxe does it the other way, so hopefully we have  
> every learning style covered. 🙂

Now we just need some magic that will direct novices to the source  
appropriate for their learning style. :-))

Kind regards

robert