On: Pure destination-passing style in Linear Haskell

[kevincox]

I've commonly seen it used for both. Really anything that the function will write to.

[masklinn → kevincox]

> I've commonly seen it used for both

That's a good reason to rename one of them because they're completely different semantics and behaviour, and confusing one for the other is a direct route to segfault city.

[comex → masklinn]

From another perspective, they're both performing the same operation on different types. With what you'd call "destination passing", like

    char *buf = malloc(128);
    snprintf(buf, 128, "hello");

the function is accepting a pointer to an uninitialized array of char, and initializing the array of char. With what you'd call an "out parameter", like

    char *buf;
    asprintf(&buf, "hello");

the function is accepting a pointer to an uninitialized pointer to array of char, and initializing the pointer. The caller still controls the allocation of storage for the pointer itself.

[arka2147483647 → masklinn]

At this point of the lifetime C-language, hoping for the commonly accepted terminology to change, is probably futile. Anyway, for out parameters, the common convention is:

Caller provides one object for output:

   void callee(Obj *obj);

Caller provides an array for output:

    void callee(Obj *obj, size_t obj_size);

Caller provides an pointer, to which callee allocates a new object:

    void callee(Obj **obj)