What is the difference between method chaining and fluent interface?
Why Interviewers Ask This
Candidates at the intermediate level are expected to not only know this concept but explain the trade-offs involved. Interviewers use this question to see if you can reason about design decisions, not just recall facts.
Answer
Method chaining is the technique of calling multiple methods in sequence on an object: $result->method1()->method2()->method3(). This works when each method returns $this (the same object) or a new object of the same type. A fluent interface is a broader design pattern built on method chaining that creates a readable, DSL-like API. PHP examples: Laravel's Query Builder (DB::table("users")->where("active", 1)->orderBy("name")->get()), Guzzle's request builder, and PHPUnit's assertion API. To implement, return $this from methods that configure the object: public function where(string $col, $val): static { $this->wheres[] = [$col, $val]; return $this; }. PHP 8 allows : static as return type for covariant return type support in subclasses.
Pro Tip
Demonstrate both theoretical understanding and practical experience. Say what it is, then give an example of how you actually used it in a PHP codebase.