c - 列表-C(作业)

所以我试图实现以下目标：；

  // Destructive Abstract data type ilist

   struct ilist_ADT;
   typedef struct ilist_ADT *ilist;
   // prototype for secret implementation
   // do not rely on ilist being a pointer

   ilist iempty();
   //    returns an empty ilist

   int iempty_huh(ilist il);
   //    returns 1 (true) if il is empty
   //    returns 0 (false) if il is not empty

   int ifirst(ilist il);
   //    returns the first element in il
   //    il must not be empty

   ilist icons_destroy(int in, ilist il);
   // returns an ilist with in added as the first element of il
   // references to il cease to be valid ilists
   // the result must eventually be consumed by one of:
   //     icons_destroy, irest_destroy, idelete

   ilist irest_destroy(ilist il);
   // modifies il to remove the first element, and returns the modified ilist
   // frees the memory associated with the first element
   // references to il cease to be valid ilists
   // the result (if non-empty) must eventually be consumed by one of:
   //     icons_destroy, irest_destroy, idelete

   ilist icopy(ilist il);
   // returns a new copy of il that continues to be a valid
   // ilist with the same elements even when il is destroyed
   // the result must eventually be consumed by one of:
   //     icons_destroy, irest_destroy, idelete

   int ilength(ilist il);
   // computes the number of elements in il

   void idelete(ilist il);
   //    frees the storage for ilist
   //    all further references to il become invalid
   //    NOTE: every ilist created by icons_destroy or
   //          irest_destroy or icopy  must eventually be destroyed
   //          by being consumed by icons_destroy or
   //          irest_destroy or idelete

我首先关注图标，我有一个非破坏性图标，例如：

ilist icons(int in, ilist il) {
   ilist r = malloc(sizeof(struct ilist_ADT));
   r->first = in;
   r->rest = il;
   r->length = 1 + ilength(il);
   return r;

}

我该怎么做才能符合实际情况呢？换句话说，我如何使它具有破坏性？

最佳答案

“破坏性”是指允许修改函数（或oop方法中的接收器）的参数。非破坏性函数表示它不修改其参数，而是返回修改后的副本。允许破坏性函数的优点是，您不必创建该副本，因此通常需要较少的malloc（在本例中，数量相同）。
在icons的实现中，您可以看到con'ing a entry使原始的ilist il保持一个有效的未修改列表！：任何使用ilist il的人都不会注意到您做了什么（当然，这只适用于单独链接的列表）。
破坏性实现首先允许您修改参数，但它也意味着您应该以有意义的方式修改参数：您应该修改它，以便仍具有对原始ilist il引用的人能够看到您的修改。你可以这样做：

// observation: the names are not the best, i would call it destructiveICons
//   (and ->first should be called ->value)
ilist icons_destroy(int in, ilist il) {
    ilist second = malloc(sizeof(struct ilist_ADT));
    second->length = il->length
    second->first = il->first
    second->rest = il->rest;
    il->length += 1;
    il->rest = second;
    il->first = in;
    return il;
}

现在，持有ilist il引用的其他人将看到新的第一个元素后面跟着旧的前一个元素。

关于c - 列表-C(作业)，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/9243475/