Bug #11772: Implicit conversion of Array in String interpolation does not call to_str

• Status: Closed
• Priority: Normal
• Assignee: -
• Target version: -
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN

[danielpclark (Daniel P. Clark)]

While providing an example in https://bugs.ruby-lang.org/issues/10930#note-7 I found that the implicit changing of an Array calls to_s without trying to_str first. Isn't String interpolation "implicitly" converting items to strings?

class Array
  def to_str
    "Hello from Array!"
  end
end

"#{[1,2,3,4,5]}"
# => [1, 2, 3, 4, 5]

I believe String interpolation should call to_str before to_s

[danielpclark (Daniel P. Clark)]

My main point here is that anything that happens within String interpolation is "implicitly" going to be a String. So shouldn't it call to_str before to_s on anything given?

class B
  def to_str
    "Hello from B"
  end
end


"#{B.new}"
# => "#<B:0x00000001969078>" 

Should work as this does.

class B
  def to_s
    "to_s"
  end
end

"#{B.new}"
# => "to_s"

I also realize that having Ruby lookup two methods to_str and then to_s may slow it down and that we don't want to make it slower. Since Ruby is optimized for to_s being called first I think it would be okay to have to_str called second. Even though by definition you would think that an "implicit" method would be the first method called.

[duerst (Martin Dürst)]

• Status changed from Open to Closed

As (implicitly) requested at ruby-core:71843.

[danielpclark (Daniel P. Clark)]

class A
  undef :to_s
  def to_str
    "hello world"
  end
end

"#{A.new}"
#NoMethodError: undefined method `to_s' for #<A:0x00000000dbea70>

"" + A.new
# => "hello world"

Using + to call to_str feels like JavaScript.