Ruby - Passing Blocks To Methods

Question

I'm trying to do Ruby password input with the Highline gem and since I have the user input the password twice, I'd like to eliminate the duplication on the blocks I'm passing in. For example, a simple version of what I'm doing right now is:

new_pass = ask("Enter your new password: ") { |prompt| prompt.echo = false }
verify_pass = ask("Enter again to verify: ") { |prompt| prompt.echo = false }

And what I'd like to change it to is something like this:

foo = Proc.new { |prompt| prompt.echo = false }
new_pass = ask("Enter your new password: ") foo
verify_pass = ask("Enter again to verify: ") foo

Which unfortunately doesn't work. What's the correct way to do this?

score 74 · Accepted Answer · edited Apr 22 '11 at 21:50

74

The code by David will work fine, but this is an easier and shorter solution:

foo = Proc.new { |prompt| prompt.echo = false }
new_pass = ask("Enter your new password: ", &foo)
verify_pass = ask("Enter again to verify: ", &foo)

You can also use an ampersand to assign a block to a variable when defining a method:

def ask(msg, &block)
  puts block.inspect
end

edited Apr 22 '11 at 21:50

BrendanDean

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answered Nov 11 '08 at 18:04

Adam Byrtek

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I had tried that initially (before asking this question), but when I do that, Highline ignores the contents of the block and dies with this error: undefined method `&' for "inputstring":String (NoMethodError) Where inputstring is what I typed in to the first prompt. – Chris Bunch Nov 11 '08 at 18:06
Sounds strange. Maybe you forgot about the comma and Ruby assumed you want to invoke method "&" on the prompt string? I've just tried the same code with HighLine and it works fine. – Adam Byrtek Nov 11 '08 at 21:13
Yea, I think I was doing ask("goo") &foo instead of ask("goo", &foo). That works now. Thanks Adam! – Chris Bunch Nov 13 '08 at 07:03
Perhaps, it would be interesting for you. http://mudge.name/2011/01/26/passing-blocks-in-ruby-without-block.html – Kirby May 16 '16 at 13:00

score 13 · Answer 2 · answered Nov 11 '08 at 19:40

13

This is how you should do it, clean and simple:

def ask(question)
    yield(question)
end

proc = Proc.new { |question| puts question }
new_pass = ask("Enter your new password: ", &proc)
verify_pass = ask("Enter again to verify: ", &proc)

answered Nov 11 '08 at 19:40

Honza

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score 4 · Answer 3 · edited Oct 11 '16 at 14:47

4

foo = Proc.new { |prompt| prompt.echo = false }
new_pass = ask("Enter your new password: ") {|x| foo.call(x)}
verify_pass = ask("Enter again to verify: ") {|x| foo.call(x)}

edited Oct 11 '16 at 14:47

nickgrim

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answered Nov 11 '08 at 17:47

David Nehme

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score 2 · Answer 4 · answered May 21 '10 at 17:48

Here is an example that will prefix the index with the yield method and append the index with the call method.

class Array
  def alter_each!
    self.each_with_index do |n, i|
      self[i] = yield(n,i)
    end
  end
  def modify_each!(add_one = true, &block)
    self.each_with_index do |n, i|
      j = (add_one) ? (i + 1) : i
      self[i] = block.call(n,j)
    end
  end
end

a = ["dog", "cat", "cow"]

a.alter_each! do |n, i|
  "#{i}_#{n}"
end

a.modify_each! false do |n,i|
  "#{n}_#{i}"
end

puts a

score -2 · Answer 5 · answered Nov 11 '08 at 17:46

I don't think the language supports a construct like this. The only way I can see to generalize this in any way is:

def foo(prompt)
  prompt.echo = false
end
new_pass = ask("Enter your new password: ") { |prompt| foo(prompt) }
verify_pass = ask("Enter again to verify: ") { |prompt| foo(prompt) }

It doesn't really shorten the code, though it does remove some duplication--if you wanted to do more than set prompt.echo to false, you'd only have to add code in one place.

Ruby - Passing Blocks To Methods

5 Answers5