Leandro Lucarella wrote:
Andrei Alexandrescu, el 18 de octubre a las 20:16 me escribiste:
Here's what I wrote to Walter:
====================
I'm going to suggest something terrible - let's get rid of T[new]. I
know it's difficult to throw away work you've already done, but
really things with T[new] start to look like a Pyrrhic victory. Here
are some issues:
* The abstraction doesn't seem to come off as crisp and clean as we
both wanted;
* There are efficiency issues, such as the two allocations that you
valiantly tried to eliminate in a subset of cases;
* Explaining two very similar but subtly different types to
newcomers is excruciatingly difficult (I'll send you a draft of the
chapter - it looks like a burn victim who didn't make it);
* Furthermore, explaining people when to use one vs. the other is
much more difficult than it seems. On the surface, it goes like
this: "If you need to append stuff, use T[new]. If not, use T[]."
Reality is much more subtle. For one thing, T[new] does not allow
contraction from the left, whereas T[] does. That puts T[] at an
advantage. So if you want to append stuff and also contract from the
left, there's nothing our abstractions can help you with.
I think this is getting overcomplicated. I don't see it as complex, I see
it like this:
2 types should be provided: array and slice.
array is a *real* type, storing and owning memory, it should be something
like this (conceptually):
class array(T)
{
size_t length;
size_t capacity;
T[capacity] elements;
}
At the point I introduce arrays I hadn't described classes.
One major problem with writing a "The X Programming Language" book is
sequencing. It's very easy to explain a complicated feature if the
listener knows all others. It is very difficult to introduce them serially.
1) a pure reference type.
2) 1 allocation only (interior pointers are not a problem, the GC have to
support them anyways).
3) easily appendable (capacity field).
slice should be something like this:
struct slice(T)
{
size_t length;
T* ptr;
}
structs and pointers have also not been introduced yet.
I'm missing something? Why this shouldn't work?
It may work, but I was unable to pull it off reasonably well.
Andrei
