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OOP PHP: What is the Double Colon in Objects/Classes for?

By byron on January 16, 2009 in PHP

php I happen to be the only PHP programmer that I know, so it’s hard to ask your buddy what the heck that :: is used for in some OO PHP programs. I know you could post it on a forum and get the answer, but I never did. And Google wasn’t really forth coming when you put :: in a search. Finally I found it in the PHP documentation: check out Scope Resolution Operator (::). In short, it’s used to access Static or Constant members of a class. Here’s a brief example:

 class DatabaseConnector {
   const CONNECTION_STRING = 'myconnectionstring';
}

//Referece that connection string constant like so...
DatabaseConnector::CONNECTION_STRING;

So there you go, mystery solved

In case you’re wondering what the :: is called, it’s a Paamayim Nekudotayim, which is Hebrew for the cryptic phrase: double colon!

Cheers,
Byron

PHP, web dev

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8 Responses to OOP PHP: What is the Double Colon in Objects/Classes for?

beanluc March 4, 2009 at 12:54 pm #

Does it do something that “->” doesn’t do?

Under what circumstancces do you use “::” but NOT “->”?

Under what circumstances will either one of them work? With ot without the same result?
Byron Bennett March 4, 2009 at 5:02 pm #

Hi beanluc,

Sounds like a test question

To use “::”, you need to be accessing static functions or variables, constants, or overridden functions. For a function, you’d need something like:

public static function showAge(){…}

then you could access it like: ClassName::showAge();

When you’re working with an instance of an object, you use ->. In general, you’ll get the same results since you’re mostly working with Constants and static functions and they don’t usually change.

Check out the link in the article above for a more details.
Cheers!
Byron
Monkey April 30, 2009 at 3:27 pm #

Thanks Byron,

I do have people I could have asked… but I was too embarassed as I should have found this out a long time ago

At least now Googling the answer works… thanks to you
Byron Bennett May 1, 2009 at 7:31 am #

Monkey,

I hear ya! Glad to help!

Byron
Daniel May 22, 2009 at 12:44 pm #

HA! Finally, a good and simple answer! Indeed, I have had such trouble googling “::”. I don’t know why, but something about giving Google a bunch of symbols doesn’t give very good search results.

Thanks for answering this question, it will come in very handy now that I know what the darn thing is and how to use it! I’ve actually asked people before, but when I ask about “that double colon thingy” I either got blank stares, or some over-technical jabbering that I could not understand.

Thanks for the great post!
Farhan April 3, 2010 at 12:57 pm #

Thanks
Mario May 12, 2010 at 8:10 pm #

thanks for posting this. i was wondering too.
yaniv July 15, 2010 at 1:35 am #

lol, I can speak hebrew so I know the paamayim nekudotaiim thingy, and thanks to you I can use it now
thanks!