Get name of lambda function as string in Ruby

Question

I have a defined a lambda function as

my_lambda = lambda { |x| 100 * x }

I am passing this function as an input to another function which needs to verify its identify, something like:

def function_verifier(func)
  if func.to_s == "my_lambda"
    return "ok"
  else
    return "mismatch!"
  end
end

However when I pass my_lambda as input to this function, the command func.to_s returns "#<Proc:0x0000a973516680@(pry):14 (lambda)>" instead of "my_lambda".

How do I turn the function handle for my_lambda into the string "my_lambda"?

Lambdas don't have names. Consider a = -> { }; b = a, what would you expect the name of the lambda to be and why? And what do you mean by "verify its identity"? — mu is too short
– mu is too short, Commented Oct 3, 2017 at 19:26
But if lambda functions don't maintain any knowledge of their name, then I'm probably better off just refactoring my code. — jon_simon
– jon_simon, Commented Oct 3, 2017 at 19:35
@jon_simon yes you are. They cannot "maintain knowledge of their name" because they don't have a name you have simply assigned one to a local variable. If you wanted to "establish that [they do] the same thing" you would have to call both of them with an equality check — engineersmnky
– engineersmnky, Commented Oct 3, 2017 at 19:38
this concept of 'original variable name' is not something we have available to us. Maybe store the lambdas in a hash, keyed by name? E.g. lambas = {foo: ->() {}} — max pleaner
– max pleaner, Commented Oct 3, 2017 at 19:52

Cary Swoveland · Accepted Answer · 2017-10-03 21:59:16Z

2

That won't work, because you are passing the proc to function_verifer and proc does not know the variable(s) whose value it is. You could do something like the following.

my_lambda = lambda { |x| 100 * x }
  #=> #<Proc:0x000000008a1790@(irb):746 (lambda)>
MY_LAMBDA_OBJECT_ID = my_lambda.object_id
  #=> 4525000

def function_verifier(func)
  func.object_id == MY_LAMBDA_OBJECT_ID ? "ok" : "mismatch!"
end

function_verifier(my_lambda)
  #=> "ok"

your_lambda = my_lambda
  #=> #<Proc:0x000000008a1790@(irb):746 (lambda)>
your_lambda.object_id
  #=> 4525000
function_verifier(your_lambda)
  #=> "ok"

my_lambda = lambda { |x| 99 * x }
  #=> #<Proc:0x000000009116d0@(irb):768 (lambda)>
my_lambda.object_id
  #=> 4754280
function_verifier(my_lambda)
  #=> "mismatch!"

edited Oct 3, 2017 at 21:59

answered Oct 3, 2017 at 20:53

Cary Swoveland

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