It was noted in another question that wrapping the result of a PHP function call in parentheses can somehow convert the result into a fully-fledged expression, such that the following works:
<?php
error_reporting(E_ALL | E_STRICT);
function get_array() {
return array();
}
function foo() {
// return reset(get_array());
// ^ error: "Only variables should be passed by reference"
return reset((get_array()));
// ^ OK
}
foo();
I'm trying to find anything in the documentation to explicitly and unambiguously explain what is happening here. Unlike in C++, I don't know enough about the PHP grammar and its treatment of statements/expressions to derive it myself.
Is there anything hidden in the documentation regarding this behaviour? If not, can somebody else explain it without resorting to supposition?
Update
I first found this EBNF purporting to represent the PHP grammar, and tried to decode my scripts myself, but eventually gave up.
Then, using phc
to generate a .dot
file of the two foo()
variants, I produced AST images for both scripts using the following commands:
$ yum install phc graphviz
$ phc --dump-ast-dot test1.php > test1.dot
$ dot -Tpng test1.dot > test1.png
$ phc --dump-ast-dot test2.php > test2.dot
$ dot -Tpng test2.dot > test2.png
In both cases the result was exactly the same: