In what way is my array index an 'Illegal string offset'?

Question

When "future-proofing" code by testing it on PHP 5.4, I get a warning I don't understand.

function __clone() {
  $this->changed = TRUE;
  foreach ($this->conditions as $key => $condition) {
    if (
    $condition['field']
    instanceOf QueryConditionInterface) {
      $this->conditions[$key]['field'] = clone($condition['field']);
    }
  }
}

I broke out $condition['field'] into its own row to reduce the amount of code to focus on. About that specific line, PHP has this to say

Warning: Illegal string offset 'field' in DatabaseCondition->__clone()

And I just can't see how 'field', is an illegal string offset. I'm guessing that I'm just missing something obvious, but if the community can't find a problem, I'll file a bug report.

I interpret the warning as "Under no circumstances is 'field' a valid key". This error would have made sense if I had tried to us for example an array as a key.

Answer 1

Without more knowledge about the creation of the conditions array/iterator, I can only assume that you should first check if the offset exists.

if(isset($condition['field']) && $condition['field'] instanceOf QueryConditionInterface)

Using isset in this situation is enough and faster than array_key_exists, the only difference is, if $condition['field'] is NULL isset will return falls, array_key_exists will return true, cause the key exists. But because you only want to work on fields that are an instance of QueryConditionInterface, you will running fine with isset.