Result of assignment is not the return value

Ruby
1

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?

2

Setters always return the value they were originally assigned

3

On Thu, Mar 11, 2010 at 6:03 PM, Yukihiro M. [email protected]
wrote:

                            matz.

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

4

Hi,

In message “Re: result of assignment is not the return value”
on Fri, 12 Mar 2010 08:55:25 +0900, Nathan B. [email protected]
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.
5

On Thu, Mar 11, 2010 at 9:39 PM, Nathan B. [email protected] wrote:

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