Question

How I can do something like this:

class Some < String
    def m1(a, b)
        self = a + b
    end
end

s = Some.new("hello")
s.m1("one ", "two")
p s # => "one two" 

Answer 1

That depends on how exactly you define “something like”.

If you want to make it so that all variables that point to the given Some object, now instead point to the string that is the result of a + b, that’s not possible.

If you want to change the string contents of the given Some object, you can use the replace method, i.e. replace(a+b).

To illustrate the difference between using replace and reassignment:

class Some < String
    def m1(a, b)
        replace( a + b )
    end
end

s1 = Some.new("hello")
p s1.object_id # some number
s1.m1("one ", "two")
p s1 # "one two"
p s1.object_id # the same number as above
p s1.class # Some

s2 = Some.new("hello")
p s2.object_id # some number
s2 = "one " + "two"
p s2 # "one two"
p s2.object_id # a different number
p s2.class # String

The latter behavior is not achievable using a method.