Question

I have the body of a ruby function as a string like

s = "x + 1"

I would like to do something like

fn = make_function(:x, s)
y = fn(10) # returns 11

What is the best way to achieve something like this?

Note that I’d rather not just keep eval’ing the string for each function call

Answer 1

This will eval the string once to define the function.

eval ['def fn(x)', s, 'end'].join("\n")

Here’s something like your desired make_function

def make_function(klass, name, args, body)
  args = [ args ].flatten.map(&:to_s).join(', ')
  klass.class_eval ["def #{name} (#{args})", body, 'end'].join("\n")
end


irb> make_function(Object,:foo,[:x],'x*2')
=> nil
irb> foo(10)
=> 20
irb> foo(1.3)
=> 2.6