RFC: scope and borrowing

[Manu via Digitalmars-d]

On 22 September 2014 13:19, Walter Bright via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:

> On 9/21/2014 4:27 AM, Manu via Digitalmars-d wrote:
>
>> It's also extremely hard to unittest; explodes the number of static if
>> paths
>> exponentially. I'm constantly finding bugs appear a year after writing
>> some code
>> because I missed some static branch paths when originally authoring.
>>
>
> If you throw -cov while running unittests, it'll give you a report on
> which code was executed and which wasn't. Very simple and useful.
>

It is a useful tool, but you can see how going to great lengths to write
this explosion of paths is a massive pain in the first place, let alone
additional overhead to comprehensively test that it works... it should
never have been a problem to start with.

You may argue that I didn't test my code effectively. I argue that my code
should never have existed in the first place. It's wildly unsanitary, and
very difficult to maintain; I can rarely understand the complexity of ref
handling code looking back after some months.

This was my very first complaint about D, on day 1... 6 years later, I'm
still struggling with it on a daily basis.

Here's some code I've been struggling with lately, tell me you think this
is right:
https://github.com/FeedBackDevs/LuaD/blob/master/luad/conversions/functions.d#L286
<- this one only deals with the return value. is broken, need to
special-case properties that receive arguments by ref, since you can't pass
rvalue->ref
https://github.com/FeedBackDevs/LuaD/blob/master/luad/conversions/functions.d#L115
<- Ref!RT workaround, because I need a ref local
https://github.com/FeedBackDevs/LuaD/blob/master/luad/conversions/functions.d#L172
<- Ref!T again, another instance where I need a ref local
https://github.com/FeedBackDevs/LuaD/blob/master/luad/conversions/functions.d#L180
https://github.com/FeedBackDevs/LuaD/blob/master/luad/stack.d#L129 <-
special case handling for Ref!T that I could eliminate if ref was part of
the type. Note: 3rd party code never has this concession...
https://github.com/FeedBackDevs/LuaD/blob/master/luad/stack.d#L448 <- more
invasion of Ref!, because getValue may or may not return ref, which would
be lost beyond this point, and it's not practical to static-if duplicate
this entire function with another version that returns ref.
https://github.com/FeedBackDevs/LuaD/blob/master/luad/stack.d#L157 <-
special-case function, again because ref isn't part of the type
There are many more instances of these throughout this code.

This is just one example, and not even a particularly bad one (I've had
worse), because there are never multiple args involved. These sorts of
things come up on most projects I've worked on.
The trouble with these examples, is that you can't try and imagine a direct
substitution of the static branches and Ref!T with 'ref T' if ref were part
of the type. This problem has deeply interfered with the code, and API
concessions have been made throughout to handle it. If ref were part of the
type, this code would be significantly re-worked and simplified. There
would probably be one little part somewhere that did logic on T, alias with
or without 'ref' as part of the type, and the cascading noise would mostly
disappear.

Add to all of that that I still can't pass an rvalue to a ref function (5
years later!!) >_<

It's also worth noting that, with regard to 'ref', the above code only
_just_ suits my needs. It's far from bug-free; there are places in there
where I was dealing with ref, but it got so complicated, and I didn't
actually make front-end use of the case in my project, that I gave up and
ignored those cases... which is not really ideal considering this is a
fairly popular library.

I have spent days trying to get this right. If I were being paid hourly, I
think I would have burned something like $2000.
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