What does PHP syntax $var1[] = $var2 mean? - php

Question

What does PHP syntax $var1[] = $var2 mean?
Note the [] after $var1 varable.

Answer 1

It means that $var1 is an array, and this syntax means you are inserting $var2 into a new element at the end of the array.
So if your array had 2 elements before, like this:
$var1=( 1 => 3, 2 => 4)
and the value of $var2 was 5, it would not look like this:
$var1=( 1 => 3, 2 => 4, 3 => 5)
It also means that if $var2 was an array itself, you have just created a two dimensional array. Assuming the following:
$var1=( 1 => 3, 2 => 4)
$var2=( 1 => 10, 2=>20)
doing a $var1[]=$var2; wouls result in an array like this:
$var1=( 1 => 3, 2 => 4, 3 => (1 =>10, 2 => 20))
As an aside, if you haven't used multi-dimensional arrays yet, accessing the data is quite simple. If I wanted to use the value 20 from our new array, I could do it in this manner:
echo $var1[3][2];
Note the second set of square brackets - basically you are saying I want to access element two of the array inside element 3 of the $var1 array.
On that note, there is one thing to be aware of. If you are working with multi-dimensional arrays, this syntax can catch you out inside a loop structure of some sort. Lets say you have a two dimensional array where you store some records and want to get more from the database:
$var1 = (
1 => (id =>1, age => 25, posts => 40),
2 => (id =>2, age => 29, posts => 140),
3 => (id =>3, age => 32, posts => 12)
)
A loop like this following:
while($row=someDatabaseRow)
{
$var1[]=$row['id']; // value 4
$var1[]=$row['age']; // value 21
$var1[]=$row['posts']; // value 34
}
will infact insert a new element for every execution, hence your array would end up looking like this:
$var1 = (
1 => (id =>1, age => 25, posts => 40),
2 => (id =>2, age => 29, posts => 140),
3 => (id =>3, age => 32, posts => 12),
4 => 4,
5 => 21,
6 => 34
)
The correct way would be to assemble the array first, then append it to your current array to maintain the strucutre, like this:
while($row=someDatabaseRow)
{
$tempArr= array();
$tempArr[]=$row['id']; // value 4
$tempArr[]=$row['age']; // value 21
$tempArr[]=$row['posts']; // value 34
$var1[]=$tempArr;
}
Now your array would look like you expected, namely:
$var1 = (
1 => (id =>1, age => 25, posts => 40),
2 => (id =>2, age => 29, posts => 140),
3 => (id =>3, age => 32, posts => 12)
4 => (id =>4, age => 21, posts => 34)
)

Answer 2

It means that you're pushing the value of var2 to array var1.

Answer 3

That's shorthand for array_push()
It will make $var1 and array (if it isn't already) and push $var2 in to it.

Answer 4

It basically makes $var1 an array and adding to it's end a value of $var2.
$var1 = NULL;
$var2 = 'abc';
$var1[] = $var2;
$var1 is now an array containing one value: 'abc'