Local TypeHinting

[steelbrain]

We can check typehint when giving providing or taking it from a function, but how can we typehint something locally?

What works already:

type User = shape('id' => int);
function OnlineStatus(User $user):void{
    DB::UserOnline($user); // this function expects a type User
}
OnlineStatus(shape('id' => 1));

btw, phpStorm uses this syntax for local type hinting

type User = shape('id' => int);
/**
 * @var User
*/
$user = shape("id" => int);
DB::UserOnline($user)

[jwatzman]

Can you give an example of a place you'd want to do this that we can't infer it? I'm really not sold on the ability to do this. (As opposed to the ability to formally declare variables, and optionally give those a type, a longer-term feature we've considered.)

[steelbrain]

type User = shape('id' => int,'name' => string, 'email' => string);

$user = shape('id' => 1,'name' => 'Steel Brain');
DB:insert('mydb.users',$user);

In the example above, the type User represent's a database table structure (they become real easy to manage with types), because this variable is local, we can not see if it's according to the Type User or not. We have to declare a function for it, that takes an input type User, and then we can do the debugging.

If we had the ability to set it's time locally, we will save ourselves one function and a lot of time!

[jwatzman]

But then wouldn't DB::insert be declared to take a second argument that has type User, and the above code would fail then? If it's inferred wrong, it's going to cause a type error as soon as you try to actually use it, and our inference is good enough to point back to the declaration site as part of the error, no type declarations needed. (Unless the code is all at toplevel! We don't typechecker anything at toplevel, and type declarations wouldn't help with that.)

[steelbrain]

DB::insert takes any kind of array object. It's not in top-level, it's in User::create.

[steelbrain]

I just thought it'd be nice, because I have to change every function that uses a database insert command whenever I update my structure, and If I forgot any of it. Then May Lord bless my Soul 😄 LOL
If this is implemented, HH_Client itself would tell me that I have missed something.

[lexidor]

Recent development for an unstable feature: typed_local_variables!

489986a

This is still an experiment. All the rules are subject to change. Even this small syntax example may change before release, if it is every released:

let $user : User = shape('id' => 1, 'name' => 'Steel Brain');

This type checks if and only if:

• All assignments to $user could pass for a User.
• If more than one let $user : ... exists in function scope:
  • Each redeclaration has the same type or a subtype of all preceding declarations.