Weird Ruby: Positive and Negative Strings

https://metaredux.com/posts/2019/05/10/weird-ruby-positive-and-negative-strings.html

by lelf • 7 years ago

37 4 7 years ago

woodruffw2• 7 years ago

The more general takeaway from this is that you can redefine (some of) Ruby's unary operators. Their naming is unfortunately less consistent than Python's dunder-methods, but each of these work: `+@` for `+`, `-@` for `-`, `~` for `~`.

Edit: Removed incorrect information.

vidarh• 7 years ago

'to_a' and * are not at all the same, and neither are 'to_proc' and '&'

unary * is the splat operator. While it tries to coerce arguments to an array, consider that this:

  x,y,z = *(1..3),42

gives x=1,y=2,z=3, while:

  x,y,z = (1..3).to_a, 42

  gives x=[1,2,3], y=42, z= nil

'&' meanwhile passes a Proc as the anonymous block to a method. E.g.:

  def foo; yield; end
  pr = proc { puts "here" }
  foo(&pr) # is equivalent to foo { puts "here" }

It too will try to coerce arguments to a proc by calling '#to_proc' on objects that responds to it, but 'to_proc' just returns a Proc (or should), it does not in itself convert a Proc to a default block. 'to_proc' has other uses - proc's can be passed around in all kinds of other situations too.

woodruffw2• 7 years ago

Yeah, I misremembered. Ruby does indeed complain when either `to_proc` or `to_a` don't return the expected types.

kentor• 7 years ago

Mutable strings was a mistake.

Weird Ruby: Positive and Negative Strings

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