I am trying to understand this simple code, if someone could explain this one section of code to a beginner. Please bear with me on the simple code and trying to understand this.
I understand what the loops are doing, it's just the !isset($value[$values]) part that's tripping me up.
Can someone explain to me what's going on with the !isset and why it's not set?
Example
$array1 = [1, 2, 3];
$array2 = [4, 5, 6];
$array3 = [7, 8, 9];
$value = [];
foreach ([$array1, $array2, $array3] as $arr) {
foreach ($arr as $values) {
if (!isset($value[$values])) { // Why is this part of the code not set?
...
}
}
}
From my understanding is:
1) $value[] Value is an empty array
2) $value[$values] You are passing in $values (1, 2, 3, 4, 5 ...) as the $key of the $value array
3) When I var_dump $value[$values] inside of the inner foreach loop I get Notice: Undefined index: Why am I getting this? The index should be the numbers right?
4) Lastly, why is $value[$values] considered not set?
$value is an empty array. Therefore, any keys that you are calling within that array will not be set, until you assign a value to that key.
$value[$values] is passing [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ], so you are calling $value[1], $value[2], etc.
You are getting undefined index because the index is undefined. PHP handles this well and issues a Notice. Other languages (Java, for example) would issue a Null Pointer Exception.
And lastly, because $value is an empty array, and that key is not set, isset() returns false. And !isset() would then return true, thus the code would execute.
When you run this code, $value is empty, so all values that you test are unset, there is no key 1, 2, 3, 4, 5 in this array... So this is why you got the undefined index error...