php中的以下语法是什么意思？

I am working on fixing some bug in legacy php code. I am not a PHP person. so please bear with me if this is a stupid question.

I see this line in the code:

$credentials = array("username"=>$fields->username, "password"=>$fields->password);
$this->profile->create($fields);

I don't understand what this syntax for array means?

I know this is associate array:

array("username"=>"mike","password"=>"123") will translate to

{  
"username": "mike",
"password" : "123"
}

but what the above one will translate to?

In the code you used for the example, $fields is an object. Then, username is a variable or property of the object. So, you end up with the array:

{
    "username": $fields->username,
    "password": $fields->password
}

If you are confused by the arrow syntax for objects, read the documentation on using objects for PHP.

$this refers to the current instance of the class that this code is in.

profile refers to the class member profile, which itself is an instance of some class.

create is a function in that class, and is now being invoked.

The variable $fields is being passed as an argument to the function.