Ruby Variable replacement inside another Variable

Question

I have a ruby variable created from a complex code , But I am unable to replace the variable declared inside my main variable . Here is an example , it may be simple but I could not able to change main variable declaration procedure.

irb(main):065:0> p msg
"My name is \#{name}"
irb(main):066:0> puts name
Foo
irb(main):067:0> puts msg
My name is #{name}
irb(main):068:0> puts "#{msg}"
My name is #{name}

I want an output like "My name is Foo" ; That needs to be achieved considering I can't control content format of variable 'msg'

Consider 'msg' is a simple variable , but It passed from a different procedure , So I cant change the declaration format . — Shan Sunny
– Shan Sunny, Commented Apr 22, 2020 at 7:43
I understand that you cannot control msg. That means you cannot use string interpolation at all. But is there any specification on how msg will look like? Like it contains always \#{name}? Or is it possible that msg might have a totally different format (like correct string interpolation) or different variables names (like fullname)? — spickermann
– spickermann, Commented Apr 22, 2020 at 7:43

peter · Accepted Answer · 2020-04-24 12:59:57Z

2

You could build your own String class with a substitution at runtime.

class StringInterpollator < String
  def replace(bind)
    gsub(/\\*#\{(\w+)\}/) do |m|
      eval($1, bind)
    end
  end
end

msg = 'My name is \#{name}'
name = "Foo"

StringInterpollator.new(msg).replace binding #My name is Foo

EDIT: here a version that accepts both local variables as instance variables

class StringInterpollator < String
  def replace(bind)
    gsub(/\\*#\{?([\w@]+)\}?/){ |m| eval($1, bind)}
  end
end

edited Apr 24, 2020 at 12:59

answered Apr 22, 2020 at 11:07

peter

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3 Comments

3limin4t0r Over a year ago

The backslash isn't in the string in the question. See the puts msg output.

Rajagopalan Over a year ago

Hi, If I pass the instance variable like #{@name}, it's not working. Should I send something else instead of binding in this case?

peter Over a year ago

puts wil not show the \, p does. Instance variables behave differently, eg they don't need the curly brackets, published a version that handles them both

xplosiveFibonacci · Accepted Answer · 2020-04-22 09:54:52Z

0

One simple approach is to use string substitution with the sub method like this

name = "Foo"
msg.sub('#{name}', name) # => "My name is Foo"

However, this assumes that msg always contains the text \#{name}

answered Apr 22, 2020 at 9:54

xplosiveFibonacci

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