Question

Let’s say I have a Ruby class:

class MyClass   def self.property     return 'someVal'   end    def self.property=(newVal)     # do something to set 'property'     success = true      return success # success is a boolean   end end 

If I try and do MyClass.property=x, the return value of the whole statement is always x. It is a convention in a lot of C-based/inspired languages to return a boolean ‘success’ value – is it possible to do this for a setter using the ‘equals syntax’ in Ruby?

Furthermore – if this isn’t possible, why not? Is there any conceivable downside to allowing an ‘equals setter’ operation return a value?

Answer 1

One downside is that you would break the chained assignment semantics:

$ irb  irb(main):001:0> x = y = 3 => 3 irb(main):002:0> p x 3 => nil irb(main):003:0> p y 3 => nil irb(main):004:0>  

Consider:

x = MyClass.property = 3 

Then x would take true if this worked as you had expected (right-associativity). That could be a surprise for people using your interface and used to the typical semantics.

You also got me thinking about parallel assignment, eg:

x, y = 1, 2 

Apparently the return value from that expression is implementation specific… I guess I won’t be chaining parallel assignments 🙂

Nice question!