How to use foreach traversal in php

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Foreach traversal

/ / write foreach ($arr as $k = > $v) {/ /} / / write two foreach ($arr as $v) {/ /} / / write three foreach ($arr as & $v) {/ /} / / write four $arr = [1, 2, 2, 3], [4, 5, 5, 6]; foreach ($arr as list ($1, 2, 6)) {/ /}

1. First of all, you need to know that $v is not addressed in method one and method two, and $v is a copy of the key value. So don't change the array / object itself in foreach, it's useless.

two。 When you don't need a keyname or index, there's nothing to say about writing $k.

3. With regard to the writing method 3 address reference assignment, the advantage is to save space when the value is very large. It is important to note, however, that either way, $v will be retained after the foreach loop, so if you are addressing it, it would be a bad thing to use $v again. The manual recommends unset ($v).

4. The fourth method is for the application of two-dimensional array / object, using list to unpack the key-value array. Note that the number of variables received in list is greater than the length in the actual two-dimensional array will report an error, less than can just not be received, so consider it when you use it.

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