Accessing an array element when returning from a f

问题:

Some searching through Google (and my own experience) shows that in PHP you can't grab an array element when it's been returned from a function call on the same line. For example, you can't do:

echo getArray()[0];

However, I've come across a neat little trick:

echo ${!${false}=getArray()}[0];

It actually works. Problem is, I don't know why it works. If someone could explain, that would be great.

Thanks.

回答1:

echo ${!${false}=getArray()}[0];

This is how it works, step by step

${false}=getArray()

assigns the result of getArray to a variable with an empty name ('' or null would work instead of false)

!${false}=getArray()

negates the above value, turning it to boolean false

 ${!${false}=getArray()}

converts the previous (false) value to an (empty) string and uses this string as a variable name. That is, this is the variable from the step 1, equal to the result of getArray.

${!${false}=getArray()}[0];

takes index of that "empty" variable and returns an array element.

Some more variations of the same idea

echo ${1|${1}=getArray()}[1];
echo ${''.$Array=getArray()}[1];

function p(&$a, $b) { $a = $b; return '_'; }
echo ${p($_, getArray())}[1];

As to why getArray()[0] doesn't work, this is because php team has no clue how to get it to work.

回答2:

it works because your using the braces to turn the value into a varialbe, heres an example.

$hello = 'test';
echo ${"hello"};

Why is this needed, this is needed encase you want to turn a string or returned value into a variable, example

${$_GET['var']} = true;

This is bad practise and should never be used IMO.

you should use Objects if you wish to directly run off functions, example

function test()
{
   $object = new stdClass();
   $object->name = 'Robert';

   return $object;
}
echo test()->name;

回答3:

It should be noted that you can do this as of PHP 5.4. From the manual on array dereferencing:

As of PHP 5.4 it is possible to array dereference the result of a function or method call directly. Before it was only possible using a temporary variable.

Example:

function theArray() {
    return range(1, 10);
}

echo theArray()[0];
// PHP 5.4+: 1
// PHP -5.4: null

Pre PHP 5.4: Attempting to access an array key which has not been defined is the same as accessing any other undefined variable: an E_NOTICE-level error message will be issued, and the result will be NULL.

Manual:

• http://www.php.net/manual/en/language.types.array.php#example-89