Comments on: Oh Ruby, who are you trying to fool?

By: jc

jc — Fri, 23 Mar 2007 17:11:46 +0000

I don’t think this is entirely true.

When you run: “5*8+5″ in IRB, it correctly returns 45. If what you say is true, it would be the equivalent of: 5.*(8.+(5)). The inner method would be called first, returning 13, and the outer method would evaluate to 13*5=65.

So there must be some ruby language magic doing the order of operation rules.

By: Frank

Frank — Fri, 23 Mar 2007 17:37:57 +0000

jc,

5*8+5 is the same as 5.*(8).+(5) which also correctly gives 45 in IRB.

But I understand what you mean. It’s true that ruby must check for the precedence of operators to correctly evaluate an arithmetic expression. So when you write : 5+8*5 , it gets transformed to 5.+((8).*(5)) instead of 5.+(8).*(5)

By: Jörg W Mittag

Jörg W Mittag — Mon, 26 Mar 2007 13:27:19 +0000

There’s a slightly more well-known example for this: the assignment operator. In Ruby, attributes are *always* private; there is *no way* to access them from the outside. (Well, I suppose you can do some meta-programming or eval’ing.) “But wait!”, I here you say, “I *can* do something like ‘foo.bar = 42′, can’t I?”. Yes, you can, but(!) that’s not an assignment (cue Henri Matisse pipe here), it’s a message send. Ruby sneakily transforms

foo.bar = 42

into

foo.bar=(42)

(Note: the equals sign is part of the message name, just like a question mark or exclamation point.)

jwm

By: Joseph Wright

Joseph Wright — Mon, 26 Mar 2007 16:05:16 +0000

> …In every single languages that I know the existence,
> every arithmetic, bitwise and conditional operators
> are built-in and global keywords.

You should learn more languages then. Smalltalk, which Ruby copies in many ways, does the same thing, treating *everything* as an object. When you define a method, it can either be infix (also called binary), which allows for e.g. ‘5 + 5′, where ‘+’ is the method; unary, which has just one argument, or keyword, which looks like ‘methodName Arg1: Arg2:’, which you might call like ‘methodName Arg1: [ code block for example] Arg2: otherarg’. I don’t know how Ruby implements this, I think there is some magic that goes on inside, like you say.

On a related note, in the “Bring your methods to life with punctuation” post, you say:
> I think ruby is the only language that allows a
> programmer to name his method logged? for example.

Not at all. Common Lisp and Scheme allow quite a few different characters, Haskell allows ‘ in its variable names, and I’m sure there are others, though none of them spring immediately to mind.

By: Augusto

Augusto — Mon, 26 Mar 2007 16:10:26 +0000

This would be more impressive, if the method declaration would have some way of specifying operator precedence. As it stands, it’s bizarre, it’s consistent because the operators are really methods but they are treated as a special case … well because they have to be.

Is there some type of well documented language spec for Ruby were these things are clearly specified (operator precedence?)

By: Frank

Frank — Mon, 26 Mar 2007 16:34:25 +0000

Jörg,

It’s funny because what you are talking about is exactly the subject of my next article. It’s all written already. I just have to publish it tonight. I hope you’ll enjoy it. I would really appreciate your comments on it.

Augusto, That’s a good question. I really don’t know if there’s some official documentation about that. Anyone knows?

By: Frank

Frank — Mon, 26 Mar 2007 17:15:20 +0000

I decided to publish the post about ruby assignments right now, just in case you are interested. (it’s on the home page)

By: Jörg W Mittag

Jörg W Mittag — Mon, 26 Mar 2007 21:25:45 +0000

I had actually started cooking up some code examples very similar to yours but figured they would be unreadable in the comments section anyway, without that nice syntax highlighting. Saved me some duplicate work (-;

jwm

By: Frank

Frank — Thu, 29 Mar 2007 20:37:57 +0000

Jörg, yeah it would have been nice if the syntax highlighter was active in the comments as well. (it might had been a little heavy on javascript though… =) )

Joseph, thanks for the info about smalltalk having the same possibility. I have updated the original post.