How to pass argument in callback function in php?

Question

I have Repository class with a method as follows:

public function GetOne($id){
    $method = __METHOD__;
    $post = null;


    $post = $this->CacheManager($method, function($id) {
        return DB::select("select * from posts where id = ?", [$id]);
    });

    return $post;
}

I want to cache the result, but in the closure/callback function the $id parameter is not working. The CacheManager is a trait where I'm using it in my repository.

public function CacheManager($method, $fn) {
  $obj = null;

  if(!$this->HasCache($method)){
    $obj = $fn();
  }else {
    $obj = $this->GetCache($method);
  }

  return $obj;
}

I have some other methods without parameters and they're working as intended.

Answer 1

Use use. :D

With the use clause, you can import variables from the parent scope into the scope of the function.

public function GetOne($id){
    $method = __METHOD__;
    $post = null;


    $post = $this->CacheManager($method, function() use ($id) {
        return DB::select("select * from posts where id = ?", [$id]);
    });

    return $post;
}

Just a side note. Since it looks you are building a caching mechanism, you will need to include the ID in the cache as well. Currently you only check by $method, but for each id you will probably have a different cache entry which may or may not exist. So I think in your function you need to do something like the line below to make the cache key more unique. I would also call the parameter $method something like $cacheKey instead, since to the cache it shouldn't be linked to a method name per se.

$method = __METHOD__ . ";$id";

Update for PHP 7.4: arrow functions

The RFC for arrow functions (AKA 'short closures') has passed voting.

With these you don't specify the parameters you want to close in, because they can only have a single expression anyway, so any expression/value they use can (and will) be taken from the parent function scope.

Since in this case the anonymous function just has a single statement, it can be rewritten into an arrow function. The call to the cache manager will then look like this:

public function GetOne($id){
    $method = __METHOD__;
    $post = null;

    $post = $this->CacheManager($method, fn() => DB::select("select * from posts where id = ?", [$id]));

    return $post;
}