(1..5) === 3 > true 3 === (1..5) > false

(1…5) === 3 > true
3 === (1…5) > false

Is this a bug or expected behavior? From my understanding it shouldn’t
matter on which side of an equal comparison an expression appears.

On Nov 15, 2007 3:25 PM, Michael C. [email protected] wrote:

(1…5) === 3 > true
3 === (1…5) > false

Is this a bug or expected behavior? From my understanding it shouldn’t
matter on which side of an equal comparison an expression appears.

Posted via http://www.ruby-forum.com/.

It’s one of those “you have to read the docs” things. The === method
for Range is left-sided because it’s a method. You can redefine it if
you want.

class Range
def ===(o)
puts o
end
end

(1…5) === 3

3

=> nil

I know it’s a method, but why doesn’t Fixnum’s === work properly with
ranges?

That should be the expected behavior, the expression is just as true one
way as it is the other.

On Nov 15, 2:56 pm, Michael C. [email protected] wrote:

I know it’s a method, but why doesn’t Fixnum’s === work properly with
ranges?

That should be the expected behavior, the expression is just as true one
way as it is the other.

What do you think “===” means? Hint: it’s not the same as “==”, or
“<<”. And it doesn’t mean “is equals to”. Obviously (1…5) does not
equal 3.

The #=== method is called in case statements, and it is up to each
class to define something reasonable.

case 3
when 1…5
puts “(1…5) === 3 means 3 is inside the range.”
when Integer
puts “Integer === 3 means that 3 is a sort of Integer”
end

Michael C. wrote:

(1…5) === 3 > true
3 === (1…5) > false

Is this a bug or expected behavior? From my understanding it shouldn’t
matter on which side of an equal comparison an expression appears.

It’s normal for the #=== operator to be asymmetric, even though it looks
symmetric. The LHS is treated as a pattern for matching the RHS.

For example:

String === “foo”

uses different criteria than

“foo” === String

and likewise for

/fo/ === “foo”

vs

“foo” === /fo/

Also, note that #=== is used in case statements.

case 3
when 1…5

end

works as you expect, because it is equivalent to

if (1…5) === 3

end

But this wouldn’t make sense:

case 1…5
when 3

end

so it really needs to be asymmetric.

Phrogz wrote:

The #=== method is called in case statements, and it is up to each
class to define something reasonable.

case 3
when 1…5
puts “(1…5) === 3 means 3 is inside the range.”
when Integer
puts “Integer === 3 means that 3 is a sort of Integer”
end

Mentally, I parse “===” as “contains”. That requires a little mental
judo for RegExps, but that’s a good thing :slight_smile:

I know it’s a method, but why doesn’t Fixnum’s === work properly with
ranges?

That should be the expected behavior, the expression is just as true one
way as it is the other.

I’m reading this as incredibly whiny, childish, and obnoxious, but
that could be totally my own perception.

The whole point of Ruby is that if you don’t want things to happen the
way they happen, you can rewrite large portions of the language -
including this piece - with very little effort. So not only is it
pointless to tell people what the language should do, but also, if you
really want the language to do that, you can make it do that with
hardly any effort at all.

Anyway. The reason threequals doesn’t behave the way you expect it to
is because you don’t know what it’s for. It’s not something you should
use in day-to-day code. It’s not an equality operator. That’s why it
doesn’t have the associative property which equality has. Threequals
is for defining how a class should be evaluated in a case/when
statement. Unless you’re defining how a class should be evaluated in a
case/when, you shouldn’t be using threequals.

So threequals is in fact working properly. You just don’t know how to
use it. The way to use it is to define a new class and then use
threequals to define how a case/when will evaluate that class. Many,
many people will never ever need to do this, because it’s a relatively
esoteric use case.

More detail, and less grumpiness:

http://gilesbowkett.blogspot.com/2007/11/what-is-threequals.html


Giles B.

Podcast: http://hollywoodgrit.blogspot.com
Blog: http://gilesbowkett.blogspot.com
Portfolio: http://www.gilesgoatboy.org
Tumblelog: http://giles.tumblr.com

On Sat, Mar 29, 2008 at 8:13 PM, Francis B. [email protected] wrote:

Is there a construct like this in Ruby?

if x in (1…5)

You can use Enumerable#include?.

if (1…5).include?(x)

Francis B. wrote:

Is there a construct like this in Ruby?

if x in (1…5)

This seems a lot more intuitive and easier to read than “(1…5) === x”,
so is it possible to modify the language to make it do that?

First of all: You usually wouldn’t use ===, you’d use (1…5).include? x
which is more readable in that it tells the reader what it does (=== is
really only used for things like case and grep - you rarely (if ever)
use
it explicitly).
To answer your question: Yes, it is:
class Object
def in?(collection)
collection.include? self
end
end

if x.in? 1…5

end

For numbers there’s also x.between?(1,5)

HTH,
Sebastian

Francis B. pisze:

if x in (1…5)

This seems a lot more intuitive and easier to read than “(1…5) === x”,
so is it possible to modify the language to make it do that?

Francis
(Ruby nuby)

Use (1…5).include? x. Ruby tends to use methods instead of abusing
keywords.

lopex

Giles B. wrote:

The whole point of Ruby is that if you don’t want things to happen the
way they happen, you can rewrite large portions of the language -
including this piece - with very little effort. So not only is it
pointless to tell people what the language should do, but also, if you
really want the language to do that, you can make it do that with
hardly any effort at all.

Is there a construct like this in Ruby?

if x in (1…5)

This seems a lot more intuitive and easier to read than “(1…5) === x”,
so is it possible to modify the language to make it do that?

Francis
(Ruby nuby)

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