Core_kernel.Heap与Core_kernel.FHeap的区别及适用场景问询

Awesome question—let’s break down what sets these two pairing heap implementations apart, and when you should reach for each one.

Core Trait: Mutable vs Persistent #

This is the biggest distinction between the two:

• Core_kernel.Heap is a mutable (imperative) heap. When you run operations like adding an element or popping the top item, it modifies the original heap in place. For example, after calling Heap.pop my_heap, my_heap itself will have one fewer element—there’s no separate "old" version left around.
• Core_kernel.FHeap is a persistent (functional) heap. Every operation (insert, pop, merge) returns a brand-new heap instance, leaving the original completely untouched. If you run let new_heap = FHeap.add old_heap item, old_heap stays exactly as it was, and new_heap is the updated version. This is the core of functional data structures—they preserve past states instead of mutating them.

Performance Tradeoffs #

• Heap wins on raw speed for single-state use cases. Since it doesn’t need to copy data to preserve old versions, operations like insert and pop have tiny constant-factor overhead. It’s optimized for scenarios where you only care about the current state of the heap.
• FHeap adds a small constant-time cost per operation to enable persistence. Each change creates new nodes as needed to keep the original heap intact, so while the asymptotic complexity (like O(log n) for most pairing heap operations) matches Heap, the actual runtime per operation is a bit higher. But this cost is worth it if you need multiple heap versions.

API & Usage Style #

• Heap follows an imperative API. You’ll call functions that modify the heap directly: Heap.add my_heap new_item (no return value needed, since my_heap is changed), and Heap.pop my_heap (returns the top element and alters my_heap). It’s intuitive if you’re working in an imperative codebase or don’t need to track past heap states.
• FHeap uses a functional API. Every operation returns a new heap, so you’ll typically assign the result to a new variable: let updated_heap = FHeap.pop old_heap. Merging heaps is also seamless here—FHeap.merge heap_a heap_b gives you a combined heap without modifying either original.

When to Use Which? #

Go with Core_kernel.Heap if: #

• You need the fastest possible heap operations and don’t need to keep old versions of the heap.
• Your code uses mutable state naturally (e.g., processing a stream where you only care about the current priority queue state).
• You’re building a straightforward priority queue where you just add items and extract min/max repeatedly, with no need to backtrack or preserve past states.

Go with Core_kernel.FHeap if: #

• You need to maintain multiple versions of the heap (e.g., in a backtracking algorithm where you might revert to a previous state, or when different parts of your code need independent heap variants).
• You’re writing functional code and prefer immutable data structures to avoid side effects.
• You frequently merge heaps and want to do so without altering the original instances.

内容的提问来源于stack exchange，提问作者ESRogs