Obtain variable value as a Ruby expression in String

Question

If I have a variable of a basic String/integer/float value, or a hash/array of these basic values, how to get its expression as a String?

If it is a string, I want '"foo"'. If it is an Integer, I want "1".

Basically I want the opposite of eval(). Currently I use inspect but it feels fragile.

Update:

I need to take user input, and output a .rb file containing that input. For exmple this erb file:

a = <%= variable %>

So if a user input a string, then in the .rb file I need to include that string in Ruby expression, e.g. a = "foo" or a = 1.

Your question is not clear to me. If it is already a string then it would return that string, if it is already an integer then it would return that integer. Therefore I do not understand the problem you are trying to solve. Would you mind elaborating and adding better examples of inputs and the expected outputs? — spickermann
– spickermann, Commented Aug 21, 2022 at 7:32
Agreed. As far as I can tell, it sounds like #inspect is exactly what you want. — Chris
– Chris, Commented Aug 21, 2022 at 7:39
@spickermann I will receive a dynamic variable from user input, and output that as part of a .rb file. Therefore I need to have that value in Ruby expression form. — lulalala
– lulalala, Commented Aug 21, 2022 at 11:41

Stefan · Accepted Answer · 2022-08-21 15:27:07Z

2

inspect is the closest built-in method available. For the types you listed (integer, float, string, array, and hash) its output resembles a literal that will evaluate to an equivalent object. It's the very same value you get from IRB when inspecting a value – those can be copy-and-pasted back into Ruby.

The only exceptions I'm aware of are Float::NAN and (+/-) Float::INFINITY which print as NaN and Infinity.

Note that you can't set any output options, though. For example, String#inspect will always use double quotes, regardless of its characters. Hash#inspect will always use the key => value "hash rocket" syntax even if all keys are symbols.

That said, a Ruby expression generated via inspect will work for those core objects but it might not generate the most succinct literals.

answered Aug 21, 2022 at 15:27

Stefan

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