When isset() should be used on Array without specifying key?
arrays, language-features, php
Solution
In PHP, `isset()` is a special form, not a function; when you call `isset($ary[$index])`, `$ary` itself doesn't have to be set first. Even with `E_STRICT`, the call won't generate a warning, because `isset` doesn't actually try to access `$ary[$index]`; it gets as far as determining that `$ary` is not set and returns `false`. So you don't need to check the array first in order to apply `isset` to an element.
Your question indicates that you know this already, and are wondering if there's a reason why you would do it anyway. The only thing I can think of is efficiency: if you're going to be checking a large number of keys for existence in an array, you can save some work by first detecting when the array itself isn't set, and just skipping all the individual key checks in that case.
Problem
I have learned that `isset($array)` is not required when checking for existence of particular key, however I also know that there is some reasons to check, without known key, if `$array` is instantiated. For example this: ``` foreach ($foo as $bar) { echo $bar; } ``` PHP Notice: Undefined variable: foo PHP Warning: Invalid argument supplied for foreach() is better this way: ``` if (isset($foo)) { foreach ($foo as $bar) { echo $bar; } } ``` As I use arrays a lot when dealing with data and I wanted to ask if there is some other cases where i should check if whole array `isset()`? Or should I just stick on checking every `$array[$key]` that I am going to use whenever known? This relates to question if there is any advantages or disadvantages on doing this: ``` if (isset($foo[0])) { foreach ($foo as $bar) { // noop } } ``` instead of this: ``` if (isset($foo)) { foreach ($foo as $bar) { // noop } } ``` So, should I ever use `isset($array)` in place of `isset($array[$key])` if `$key` is known?