peekfront

Peekfront is an operation associated with queue-like data structures that returns the element at the front of the queue without removing it. It allows inspecting the next item to be processed while keeping the queue’s state unchanged.

Behavior and edge cases: If the queue is non-empty, peekfront returns the front element as a value. If the queue is empty, the operation typically returns a special value such as null or raises an underflow exception, depending on the language or library. The method may be called peek or front in different implementations. It is distinct from dequeue or remove operations, which remove and return the front element.

Performance: Peekfront is usually implemented to run in constant time, O(1), since it simply accesses the first stored element. Memory usage does not require additional space beyond the queue’s own storage.

Usage and semantics: Peekfront is useful in loops or decision points where the next item must be examined before deciding whether to enqueue or dequeue. In multi-threaded or concurrent contexts, implementations may offer atomic or blocking variants to ensure safe inspection when multiple producers or consumers are present.

Language notes: The exact naming and behavior vary by library and language. For example, Java’s Queue interface provides a peek() method that returns the head or null if empty; C++ std::queue.front() accesses the first element but has undefined behavior if called on an empty queue; Python’s collections.deque allows peeking via indexing (dq[0]) but does not define a separate peek method.

Related terms: front, peek, dequeue, enqueue. The concept is common across many queue implementations, though the exact API and error handling differ.