Here you can see all the rules in action: $a = The merging procedure applies the rules key by key. Use Case 4: Mixed Key TypesĪrrays with mixed key types do not change anything about the rules explained above. ℹ️ For matching string keys, + takes the value from the left-hand side, array_merge takes the value from the right-hand side. Now, array_merge behaves differently: when a string key matches, the value from $b is taken. The + operator handles string keys the same way, it handled numeric keys: when a key matches, the value from $a is taken. Let's move on and see how + and array_merge handle arrays with string keys. ⚠️ If you need to preserve numeric keys, array_merge will not work. array_merge actually renumbers the numeric keys, starting at zero. When a key matches, the value from $a has priority.Īt a first glance, the result of array_merge looks similar like before, but notice that the keys changed.
The + operator's result is consistent with what we learned previously. Use Case 2: Numeric Keysīut what happens if we use numeric keys, which do not start at zero? $a = 👉 To append two "normal" arrays, use array_merge. ⚠️ Because the implicit keys match, the + operator only uses the values from the left-hand side.Īrray_merge appends values for numeric keys: we get what we expect from an "append" function. Let's see how the + operator and array_merge perform on "normal" arrays: $a = // = What are "normal" arrays in PHP? They are arrays with numeric keys, starting at zero: is a shortcut for. 👉 As we'll see, this makes array_merge more geared towards handling "normal" arrays.
Because this behavior cannot preserve the keys, the resulting numeric keys are renumbered. If a string key occurs in both arrays, the value from the right-hand side is used.īut if a numeric key matches, the corresponding value from the right-hand side is appended. Again, array_merge($a, $b) appends $b to $a. The built-in function array_merge is similar, but a bit more intricate. 👉 The + operator is more intuitive for arrays with explicit keys. The type of the keys is ignored: numeric and string keys are treated the same way and the keys are always preserved. But if a key occurs in both arrays, only the value from the left-hand side is used. When computing $a + $b, $b is appended to $a. The + operator, applied to arrays is also called the union operator. But for those of you who are interested in the details, let's dive right into it.
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