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POHow to find the next numeric index of an existing array?
 

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  1. POHow to find the next numeric index of an existing array?
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    <p>I'm looking for a simple way to obtain the next numerical index of an array for a new element that would have been chosen by PHP as well.</p> <p><strong>Example 1:</strong></p> <pre><code>$array = array(); $array[] = 'new index'; </code></pre> <p>This would be 0 for this case.</p> <p><strong>Example 1a:</strong></p> <pre><code>$array = array(100 =&gt; 'prefill 1'); unset($x[100]); $x[] = 'new index'; </code></pre> <p>This would be 101 for this case.</p> <p><strong>Example 2:</strong></p> <pre><code>$array = array(-2 =&gt; 'prefill 1' ); $array[] = 'new index'; </code></pre> <p>This would be 0 again for this case.</p> <p><strong>Example 3:</strong></p> <pre><code>$array = array(-2 =&gt; 'prefill 1', 1 =&gt; 'prefill 2' ); $array[] = 'new index'; </code></pre> <p>This would be 2 for this case.</p> <p>I'd like now to know the next numerical key that PHP would have chosen as well for the new element in the array but w/o iterating over all the arrays values if possible.</p> <p>I need this for a own array implementation via the SPL that should mimic PHP default behavior if a new element is added w/o specifying the offset.</p> <p><strong>Example 4:</strong></p> <pre><code>$array = array(-2 =&gt; 'prefill 1', 'str-key-1' =&gt; 'prefill 2', 1 =&gt; 'prefill 3' , 'str-key-2' =&gt; 'prefill 4'); $array[] = 'new index'; </code></pre> <p>This would be 2 for this case again.</p> <p><strong>Example 5:</strong></p> <pre><code>$array = array(-2 =&gt; 'prefill-1', 'str-key-1' =&gt; 'prefill-2', 1 =&gt; 'prefill-3' , '5667 str-key-2' =&gt; 'prefill-4'); $array[] = 'new index'; </code></pre> <p>This would be 2 for this case as well.</p> <p>Update: I've added more examples to show some of the edge cases.</p>
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    1. CONote that this is not possible to do accurately without knowing the history of the array. (See my answer.) Does that matter?
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    2. COYes it does matter and as you answered, this problem is technically not solvable from PHP userspace because there is no helper function or datastructure that allows to access `->nNextFreeElement`. The only way to get it is to add an element and then read out the value from the added element. So that's a way to access that property but it also implies to modify the array.
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