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From: Julio Di Egidio <julio@diegidio.name>
Newsgroups: comp.lang.c
Subject: Re: So You Think You Can Const?
Date: Wed, 8 Jan 2025 17:24:05 +0100
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On 08/01/2025 17:05, Julio Di Egidio wrote:
> On 08/01/2025 16:16, Ben Bacarisse wrote:
<snip>
>> More relevant to a discussion of const is to ask what you plan to do
>> with pT since you can't (without a cast) assign any useful value to the
>> allocated object.
> 
> Say my program unit implements AVL trees, with (conceptually speaking) 
> constructors/destructors, navigation and retrieval, and of course 
> manipulation (inserting, deleting, etc.).
> 
> My idea (but I would think this is pretty "canonical" and, if it isn't, 
> I am missing the mark) is: my public functions take/give "sealed" 
> instances (with const members to const data), as the user is not 
> supposed to directly manipulate/edit the data, OTOH of course my 
> implementation is all about in-place editing...

P.S.  To be clear, as I am still being a bit quick: I do not also mean 
"public destructors" should take a const pointer in input, i.e. apply as 
appropriate...

And here is what my construction/destruction code is looking like at the 
moment, which should also make clear what I meant by "a private method 
implementing a public interface" and why:

```c
static AvlTree_t const *AvlTree_node(
     void const *pk, AvlTree_t const *pL, AvlTree_t const *pR
) {
     AvlTree_t *pT;

     pT = malloc(sizeof(AvlTree_t));

     if (!pT) {
         return NULL;
     }

     pT->pk = pk;
     pT->pL = pL;
     pT->pR = pR;

     return pT;
}

static int AvlTree_free_(AvlTree_t const *pT) {
     assert(pT);

     free((AvlTree_t *)pT);

     return 0;
}

AvlTree_t const *AvlTree_create(void const *pk) {
     return AvlTree_node(pk, NULL, NULL);
}

void AvlTree_destroy(AvlTree_t *pT) {
     AvlTree_visitPost(AvlTree_free_, pT);
}
```

-Julio