A brief discussion of PHP source code twenty-two: About the array_splice function

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A brief discussion on PHP source code Twenty-two: About the array_splice function
array_splice
(PHP 4, PHP 5)

array_splice - remove part of the array and replace it with other values
Explanation
array array_splice (array &input, int offset [, int length [, array replacement]] )

array_splice() Remove the cells specified by offset and length in the input array. If the replacement parameter is provided, use the cells in the replacement array. replace. Returns an array containing the removed cells. Note that numeric key names in input are not preserved.

If offset is positive, removal starts from the offset specified by the value in the input array. If offset is negative, removal begins at the offset specified by this value from the end of input.

If length is omitted, all parts of the array from offset to the end are removed. If length is specified and is positive, this many cells are removed. If length is specified and is negative, all elements from offset to length counting down from the end of the array are removed. Tip: To remove all elements from offset to the end of the array when replacement is given, use count($input) as length.

If a replacement array is given, the removed cells are replaced by cells in this array. If the combination of offset and length results in no value being removed, the element in the replacement array will be inserted at the position specified by offset. Note that the key names in the replacement array are not retained. If the value used to replace is just a unit, then there is no need to add array() to it, unless the unit itself is an array.

The array_splice function calls the php_splice function. The main code description of this function is as follows :

 /* 创建并初始化返回数组，此返回数组为php_splice的返回数组，并非array_splice的返回数组（array_splice的返回数组为removed）*/ALLOC_HASHTABLE(out_hash);    zend_hash_init(out_hash, 0, NULL, ZVAL_PTR_DTOR, 0);/*将数组中从开始到offset的元素拷贝到返回数组中 */for (pos=0, p=in_hash->pListHead; pos<offset && p ; pos++, p=p->pListNext) { 
    entry = *((zval **)p->pData);
    entry->refcount++;/*更新返回数组 */if (p->nKeyLength)
    zend_hash_quick_update(out_hash, p->arKey, p->nKeyLength, p->h, &entry, sizeof(zval *), NULL);else
    zend_hash_next_index_insert(out_hash, &entry, sizeof(zval *), NULL);}/* 将需要移除的元素赋值给removed，即array_splice的返回数组 */if (removed != NULL) {
    for ( ; pos<offset+length && p; pos++, p=p->pListNext) {
    entry = *((zval **)p->pData);
    entry->refcount++;
    if (p->nKeyLength)
        zend_hash_quick_update(*removed, p->arKey, p->nKeyLength, p->h, &entry, sizeof(zval *), NULL);
    else
        zend_hash_next_index_insert(*removed, &entry, sizeof(zval *), NULL);
    }} else /* 其它情况，跳过这些元素 */
    for ( ; pos<offset+length && p; pos++, p=p->pListNext);/* 如果有元素需要插入，即有replacement参数 */if (list != NULL) {/* 对于每个元素，创建新的zval，拷贝并将它写入到返回数组中*/
    for (i=0; i<list_count; i++) {
        entry = *list[i];
        entry->refcount++;
        zend_hash_next_index_insert(out_hash, &entry, sizeof(zval *), NULL);
    }}/* 拷贝剩下的元素 */for ( ; p ; p=p->pListNext) {
    entry = *((zval **)p->pData);
    entry->refcount++;
    if (p->nKeyLength)
        zend_hash_quick_update(out_hash, p->arKey, p->nKeyLength, p->h, &entry, sizeof(zval *), NULL);
    else
        zend_hash_next_index_insert(out_hash, &entry, sizeof(zval *), NULL);} /* 重置数组的游标，相当于reset函数*/zend_hash_internal_pointer_reset(out_hash);

The whole process:
1. Copy the elements from the start to offset to the return array
2. Remove the elements from offset to offset+length
3. If there are replaced elements , insert the new element into the position after offset
4. Insert the function after offset length into the back of the returned array
5. Reset the array cursor

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