How to access variable using a Ruby method call?

Question

I am new to Ruby and don't know how to access data members within a function (syntax-wise). Here is my question. I have a function that will put values into an array of numbers, from a user given range, that are prime. The function looks like so:

#Search for primes within a range
def find_primes(starting, ending)

    #Make an empty array
    a = []

    for x in starting..ending
        if is_prime(x)
            a << x #Store results in array
        end
    end

    yield
end

The catch is that I must use the yield keyword to call another function to get the data from array 'a'. For example, I need to print out consecutive prime numbers, that are stored in 'a', and I have this code to do this (except I don't know how to get at the values of 'a' from the code below. This is called closure, I believe)

find_primes(0,50) do 

    i = 0

    while i < a.size - 1
        print "[#{a[i]} #{a[i+1]} "
    end
end

This is all very new to me and I can't find a good source on how to do what I am tasked to do. Thank you in advance

good to see - Prime also.

Arup Rakshit
– Arup Rakshit

2014-02-25 18:18:25 +00:00
Commented Feb 25, 2014 at 18:18 — Arup Rakshit
– Arup Rakshit, Commented Feb 25, 2014 at 18:18

sawa · Accepted Answer · 2014-02-25 18:53:19Z

1

You have a whole wrong idea. Using for in Ruby is code smell. This is how you do it if you want the iterator built in:

def find_primes(starting, ending, &pr)
  (starting..ending).select{|x| is_prime(x)}.each(&pr)
end

find_primes(1, 10){|x| puts x}

But the code above lacks flexibility. For flexibility, you should just make it return an array (or an enumerator). Then, you can use different iterators:

def find_primes(starting, ending)
  (starting..ending).select{|x| is_prime(x)}
end

find_primes(1, 10).each{|x| puts x}
find_primes(1, 10).each_cons(2){|x, y| puts "#{x} #{y}"}

edited Feb 25, 2014 at 18:53

answered Feb 25, 2014 at 18:16

sawa

169k51 gold badges287 silver badges398 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

reZach Over a year ago

I believe you have the wrong idea, I need to pass in a block of code into the function 'find_primes' implicitly to manipulate the data. Even if this is inefficient, its the way I was told to do this

sawa Over a year ago

What do you mean by "implicitly pass in a block of code"?

reZach Over a year ago

I take back my previous comment, I think you did in fact answer this but I didn't recognize it. Ruby syntax problems.

Daniël Knippers · Accepted Answer · 2014-02-25 18:29:45Z

0

If you want to return the variable a to the block you should use yield a instead of yield, then you can use find_primes like so:

require 'prime'

def find_primes(from, to)
  yield (from..to).select { |n| Prime.prime? n }
end

find_primes(0, 10) do |primes|
  p primes # => [2, 3, 5, 7]
end

Having said that, you can just use find_primes to return the array like a normal method if you want. You don't have to use yield with blocks. That is:

def find_primes(from, to)
  (from..to).select { |n| Prime.prime? n }
end

primes = find_primes(0,10)
# Do something with primes

answered Feb 25, 2014 at 18:29

Daniël Knippers

3,0551 gold badge14 silver badges17 bronze badges

Collectives™ on Stack Overflow

How to access variable using a Ruby method call?

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related