code: func (h *HashMap) Put(k T, v T) {
  	hash := h.hash(k)
  	head := h.table[hash]
  	for entry := head; entry != nil; entry = entry.next {
  		if h.eq(entry.k, k) {
  			entry.v = v
  			return
  		}
  	}
  	h.table[hash] = &hashEntry{k: k, v: v, next: head}
  	h.size++
  }
docs: // Put inserts a key/value pair into this HashMap. If the key is already present, the existing
  // value is overwritten.