Why does respond_to? need symbols as arguments in Ruby?

Question

Why does this method only accept symbols and not strings as its arguments?

x = 10
x.respond_to?(next)

Pushing a string like the above would throw (ruby):1: void value expression.

score 3 · Accepted Answer · answered Jun 01 '15 at 06:43

3

It does accept strings:

x = 10
x.respond_to?('next')
# => true

Your problem is that you didn't pass string, but next keyword.

answered Jun 01 '15 at 06:43

Marek Lipka

So, it's interchangeable? – qedk Jun 01 '15 at 06:44
`'next'` string and `:next` symbol? Yes, in this context. – Marek Lipka Jun 01 '15 at 06:45
Another side question, are single quotes are interchangeable with double quotes? In Java, they're only used with char. – qedk Jun 01 '15 at 06:45
@therewillbecoffee http://stackoverflow.com/questions/6395288/double-vs-single-quotes – Marek Lipka Jun 01 '15 at 06:46

Vitalii Elenhaupt · Answer 2 · 2015-06-01T07:02:28.750

1

From Ruby respond_to? doc:

respond_to?(symbol, include_all=false) → true or false 
respond_to?(string, include_all=false) → true or false

It accepts both, symbol and string. And if string passed it is converted to a symbol.

As mentioned by Marek, you didn't pass string, neither symbol and have a syntax error with built-in keyword.

edited Jun 01 '15 at 07:02

answered Jun 01 '15 at 06:55

Vitalii Elenhaupt

2 Answers2