Detect infinite recursion?

Question

Lets assume I have a function that crawls over an array...

flatten([a, b, c, d, [e, f, g, [h, i, j, k], l], m, n, o, p])
>> [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p]

Flatten would crawl over the code and for each array encountered would recursively enter into that array and return the values such that you have a flat array.

This works until we have an array such as:

a    = [];
a[0] = a;

This obviously creates infinite recursion:

Array[1]
0: Array[1]
 0: Array[1]
  0: Array[1]
   0: Array[1]
    0: Array[1]
     0: Array[1]
      ...

How can I detect this behavior without modifiying the array such that the function can deal with this?

Answer 1

If detecting recursion is a requirement, you're going to have to trade memory space for it: create an array of objects you parsed (the parameters you send recursively) and check each new parameter against it. If you already parsed it, return immediately.