Why class returns `null` but the definition not when their description ended in IRB?

ruby-talk
1

The below class description returns its last evaluated expression :

class A
1+7
2+4
end

=> 6

To return `6` which method the expression generally called?

But why the definition always `nil` ?

def D
3+5
end

=> nil

···

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2

Because that's how it is implemented.

···

2013/3/1 Kumar R. <lists@ruby-forum.com>

The below class description returns its last evaluated expression :

>> class A
>> 1+7
>> 2+4
>> end
=> 6

To return `6` which method the expression generally called?

But why the definition always `nil` ?

>> def D
>> 3+5
>> end
=> nil

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

3

Thanks to all you people.. :slight_smile: BTW i put the subject wrongly. :frowning: forgive
me for that.

···

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4

To be more explicit. The class is evaluated at definition, a method is
evaluated when it is run.

···

2013/3/1 Matt Mongeau <halogenandtoast@gmail.com>

Because that's how it is implemented.

2013/3/1 Kumar R. <lists@ruby-forum.com>

The below class description returns its last evaluated expression :

>> class A
>> 1+7
>> 2+4
>> end
=> 6

To return `6` which method the expression generally called?

But why the definition always `nil` ?

>> def D
>> 3+5
>> end
=> nil

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

5

When a class or module is defined, the code inside is evaluated and the
return value of the last expression is returned. This is because you could
define class level attributes or constants or execute arbitrary code
relevant to the class or to prepare it.

When a method is defined as in your second example, the code inside is only
executed when the method is run. You could call the D() method to return 8
as expected.

Is that helpful?

···

On Fri, Mar 1, 2013 at 11:38 AM, Matt Mongeau <halogenandtoast@gmail.com>wrote:

Because that's how it is implemented.

2013/3/1 Kumar R. <lists@ruby-forum.com>

The below class description returns its last evaluated expression :

>> class A
>> 1+7
>> 2+4
>> end
=> 6

To return `6` which method the expression generally called?

But why the definition always `nil` ?

>> def D
>> 3+5
>> end
=> nil

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

--
Ryan Cook
720.319.7660

6

Oops! Right on Matt -- beat me to it.

···

On Fri, Mar 1, 2013 at 11:51 AM, Ryan Cook <cookrn@gmail.com> wrote:

When a class or module is defined, the code inside is evaluated and the
return value of the last expression is returned. This is because you could
define class level attributes or constants or execute arbitrary code
relevant to the class or to prepare it.

When a method is defined as in your second example, the code inside is
only executed when the method is run. You could call the D() method to
return 8 as expected.

Is that helpful?

On Fri, Mar 1, 2013 at 11:38 AM, Matt Mongeau <halogenandtoast@gmail.com>wrote:

Because that's how it is implemented.

2013/3/1 Kumar R. <lists@ruby-forum.com>

The below class description returns its last evaluated expression :

>> class A
>> 1+7
>> 2+4
>> end
=> 6

To return `6` which method the expression generally called?

But why the definition always `nil` ?

>> def D
>> 3+5
>> end
=> nil

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

--
Ryan Cook
720.319.7660

--
Ryan Cook
720.319.7660