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From: Nathan Beyer on 11 Mar 2010 18:55
Given a simple class like this

class MyClass
attr_reader :value
def value=(val)
@value = val.to_s
end
end

Why the the following code return the value passed and not the value
assigned?

c = MyClass.new
result = c.value = 2
puts result
puts c.value

This is currently outputing

2
"2"

The results are the same when MyClass is modified to be this.

class MyClass
attr_reader :value
def value=(val)
@value = val.to_s
return @value
end
end

Shouldn't the result of the 'value=' method be the return value?

From: Tony Arcieri on 11 Mar 2010 18:57
[Note: parts of this message were removed to make it a legal post.]

Setters always return the value they were originally assigned

On Thu, Mar 11, 2010 at 4:55 PM, Nathan Beyer <nbeyer(a)gmail.com> wrote:

> Given a simple class like this
>
> class MyClass
> attr_reader :value
> def value=(val)
> @value = val.to_s
> end
> end
>
> Why the the following code return the value passed and not the value
> assigned?
>
> c = MyClass.new
> result = c.value = 2
> puts result
> puts c.value
>
> This is currently outputing
>
> 2
> "2"
>
> The results are the same when MyClass is modified to be this.
>
> class MyClass
> attr_reader :value
> def value=(val)
> @value = val.to_s
> return @value
> end
> end
>
> Shouldn't the result of the 'value=' method be the return value?
>
>


--
Tony Arcieri
Medioh! A Kudelski Brand

From: Yukihiro Matsumoto on 11 Mar 2010 19:03
Hi,

In message "Re: result of assignment is not the return value"
on Fri, 12 Mar 2010 08:55:25 +0900, Nathan Beyer <nbeyer(a)gmail.com> writes:

|Shouldn't the result of the 'value=' method be the return value?

It's a design choice. We defined the value of the assignment as the
value of the right hand expression, not the return value from the
assigning method.

matz.

From: Nathan Beyer on 11 Mar 2010 22:39
On Thu, Mar 11, 2010 at 6:03 PM, Yukihiro Matsumoto <matz(a)ruby-lang.org> wrote:
> Hi,
>
> In message "Re: result of assignment is not the return value"
>    on Fri, 12 Mar 2010 08:55:25 +0900, Nathan Beyer <nbeyer(a)gmail.com> writes:
>
> |Shouldn't the result of the 'value=' method be the return value?
>
> It's a design choice.  We defined the value of the assignment as the
> value of the right hand expression, not the return value from the
> assigning method.
>
>                                                        matz.

Ahh. Thanks. I figured it was something like that, but I couldn't find
any concrete reference to it.

>
>

From: Hal Fulton on 12 Mar 2010 02:30
[Note: parts of this message were removed to make it a legal post.]

On Thu, Mar 11, 2010 at 9:39 PM, Nathan Beyer <nbeyer(a)gmail.com> wrote:

> On Thu, Mar 11, 2010 at 6:03 PM, Yukihiro Matsumoto <matz(a)ruby-lang.org>
> wrote:
> >
> > It's a design choice. We defined the value of the assignment as the
> > value of the right hand expression, not the return value from the
> > assigning method.
> >
> > matz.
>
> Ahh. Thanks. I figured it was something like that, but I couldn't find
> any concrete reference to it.
>
>
I have thought about this for awhile. One rationalization is this.

Think of "stacked assignment" which Ruby borrows from C.

x = y = 5

An accessor acts much like a simple assignment:

x = foo.bar = 5 # same as: x = (foo.bar = 5)

In this case, it would be weird if x ended up being anything
other than 5.


Hal

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