Not too long ago, there was a thread about a bug in Ruby where vectors

(which turned out to be derived from matrices) failed to work as hash

keys.

The problem turned out to be a typo in the definition of the Matrix

class.

The method “eql?” is used by hashes for key comparison but, in the

Matrix

class, this method was named “eqn?” by mistake.

This got me thinking about the role of the “eql?” method. Why does

it

exist? What is the Ruby rationale behind having two different equality

methods, namely “==” and “eql?”

Thank you…

Just Another Victim of the Ambient M. wrote:

`This got me thinking about the role of the "eql?" method. Why does it`

exist? What is the Ruby rationale behind having two different equality

methods, namely “==” and “eql?”

Thank you…

ri Object#eql?

```
...
The +eql?+ method returns +true+ if _obj_ and _anObject_ have the
same value. Used by +Hash+ to test members for equality. For
objects of class +Object+, +eql?+ is synonymous with +==+.
Subclasses normally continue this tradition, but there are
exceptions. +Numeric+ types, for example, perform type conversion
across +==+, but not across +eql?+, so:
1 == 1.0 #=> true
1.eql? 1.0 #=> false
```

Greetings,

Esad

On 10/19/06, Just Another Victim of the Ambient M.

[email protected] wrote:

`Not too long ago, there was a thread about a bug in Ruby where vectors`

(which turned out to be derived from matrices) failed to work as hash keys.

The problem turned out to be a typo in the definition of the Matrix class.

The method “eql?” is used by hashes for key comparison but, in the Matrix

class, this method was named “eqn?” by mistake.

This got me thinking about the role of the “eql?” method. Why does it

exist? What is the Ruby rationale behind having two different equality

methods, namely “==” and “eql?”

Most languages provide many equality operators,

as depending on context different kind of “equality” is needed.

Obviously we want 1.0 == 1 to be true, right ?

And as obviously, we want a_hash[1.0] and a_hash[1] to be different.

So we have == and eql?, and even equal? for “is-it-the-same-object”.