Why does `defined?` return a string or nil?

Question

In ruby, why would defined? return a string? Most other ruby methods ending with a ? return a boolean.

Was this a hack to support a feature req

Answer 1

No, it was neither a hack nor a misuse of Ruby convention. As matz writes in ruby-talk 7986:

The '?' methods ... return either

• (a) true or false
• (b) non-false informative value or nil

defined? falls into (b).

Also, as commenters have pointed out, defined? is not a method. Matz expands in ruby-talk 1637:

[defined? is] a control structure. Not everything is a message send in Ruby, e.g. control structures, variables, blocks are not objects. defined? is among these things.