When does a function in a variable get called in PHP?

Question

There is no problem here but this has been on my mind and I couldn't find the answer anywhere. If I have a variable being populated with a function, does the function only get called when that variable is referenced? Here's and example:

function foo(){

    $foo = "Foo";
    return $foo;

}

$foo = foo();

echo $foo;

In that example I am referencing $foo outside of the function with echo. If I weren't to reference that variable would foo() still be called?

I guess it doesn't really matter I was just wondering.

When you say $foo = foo();, you're saying assign that variable to the result of evaluating that function. It will assign it right then and there, so yes, the function will be run. — ಠ_ಠ
– ಠ_ಠ, Commented Jun 15, 2013 at 23:29

transilvlad · Accepted Answer · 2013-06-15 23:29:32Z

4

The function gets called when the variable is created.

When a variable is created it's contents is evaluated and memorized.

This is the best I can explain the process :)

answered Jun 15, 2013 at 23:29

transilvlad

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2 Comments

evan.stoddard Over a year ago

That's what I was thinking. Thanks for the time.

Aaron Saray Over a year ago

I like to also remember that evaluation is done from right to left on assignment, and left to right on comparison. :)

Lawrence Cherone · Accepted Answer · 2013-06-16 00:03:52Z

1

PHP parses the full source,to check for syntax errors and then produces the tokenized form of the script into memory. This is then interpreted during the execution phase. The value of a token is the bytecode/opcode value that represent what action to perform within the life cycle of the processing thread.

$foo - In your example there is 2 independent $foo variables (there not the same) in memory there is a reference to the $foo in your function and the $foo outside the functions scope.
foo() - The foo function is called when the thread cycle hits $foo = foo();, the opcodes for the foo function are loaded into memory on script initialisation.

edited Jun 16, 2013 at 0:03

answered Jun 15, 2013 at 23:57

Lawrence Cherone

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