Question

Why does ruby addition cannot coerce given string to fixnum and vice verca?

irb>fixnum = 1
=> 1
irb> fixnum.class
=> Fixnum
irb> string = "3"
=> "3"
irb> string.class
=> String
irb> string.to_i
=> 3
irb> fixnum + string
TypeError: String can't be coerced into Fixnum
    from (irb):96:in `+'
    from (irb):96
    from :0
irb(main):097:0> 

Answer 1

Because ruby doesn’t know whether you want to convert the string to int or the int to string. In e.g. java 1 + "3" is "13". Ruby prefers to raise an error, so that the user can decide whether to to_s the one operand or to_i the other, rather than doing the wrong thing automatically.