On 1/26/2017 5:42 AM, Dicebot wrote:
> https://issues.dlang.org/show_bug.cgi?id=17123
>
> Can I have my "I told you so" badge please?

Yes, you may. But nobody promised there would be no regressions - just that we'll fix them. I'll see about taking care of this one. Thanks for reporting it.

On 1/27/2017 3:12 AM, Dicebot wrote:
> And also stuff like https://github.com/dlang/druntime/pull/1740

I'm curious what is wrong with that?


> I think the
> story behind `return scope` is the critical point for me. It is worst technical
> disaster that has happened to compiler in years, and I am going to blame Walter
> personally for it.

Yes, I'm 100% responsible for 'return scope' and pushing it harder than most people probably would like. Maybe I'm alone, but I strongly believe it is critical to D's future.

On Friday, 27 January 2017 at 19:09:30 UTC, Walter Bright wrote:
> On 1/26/2017 5:42 AM, Dicebot wrote:
>> https://issues.dlang.org/show_bug.cgi?id=17123
>>
>> Can I have my "I told you so" badge please?
>
> Yes, you may. But nobody promised there would be no regressions - just that we'll fix them. I'll see about taking care of this one. Thanks for reporting it.

Regressions are the symptoms.

I mostly went silent on this because I this point, I have no idea how to reach to you and Andrei. This is bad because of all the same reasons inout is bad, plus some other on its own, and is going down exactly like inout so far, plus some extra problems on its own.

On Friday, 27 January 2017 at 19:12:37 UTC, Walter Bright wrote:
> Yes, I'm 100% responsible for 'return scope' and pushing it harder than most people probably would like. Maybe I'm alone, but I strongly believe it is critical to D's future.

You sound like this guy: http://www.drdobbs.com/cpp/type-qualifiers-and-wild-cards/231902461

On 1/27/2017 4:43 PM, deadalnix wrote:
> I mostly went silent on this because I this point, I have no idea how to reach
> to you and Andrei. This is bad because of all the same reasons inout is bad,
> plus some other on its own, and is going down exactly like inout so far, plus
> some extra problems on its own.


If you've got a case, make it. If you see problems, explain. If you want to help, please do.

On Saturday, 28 January 2017 at 03:40:43 UTC, Walter Bright wrote:
> On 1/27/2017 4:43 PM, deadalnix wrote:
>> I mostly went silent on this because I this point, I have no idea how to reach
>> to you and Andrei. This is bad because of all the same reasons inout is bad,
>> plus some other on its own, and is going down exactly like inout so far, plus
>> some extra problems on its own.
>
>
> If you've got a case, make it. If you see problems, explain. If you want to help, please do.

I did so repeatedly for years and never reached to you or Andrei, so I'm not sure how that's going to change anything but here you go.

The root problem you are trying to solve is to be able to specify that what comes out of a function has a common property with what come in. In the case of inout, this property is the type qualifier, in the case of return/scope this is the lifetime.

Same problem, same solution, same fallout.

On Saturday, 28 January 2017 at 03:40:43 UTC, Walter Bright wrote:
> If you've got a case, make it. If you see problems, explain. If you want to help, please do.

So, do what numerous people have done numerous times already, to no great effect?

On Saturday, 28 January 2017 at 03:40:43 UTC, Walter Bright wrote:
> If you've got a case, make it. If you see problems, explain. If you want to help, please do.

For what it's worth, here are my problems with 'return scope':

- As far as I can tell, it's not properly documented. The github page for DIP-1000 is apparently pending a rewrite, and I can't find a formal definition of 'return scope' anywhere (the D reference 'Functions' page only mentions 'return ref', and in passing).

- I personally don't like using the return keyword as anything but an instruction; when I'm reading code, I can have a good feeling of the code's flow by just looking at the indentation, the if/while/for blocks, and the break/throw/return instructions. I'll be the first to admit it's kind of minor though.

- It's an obvious monkey patch, and it will clearly have to be replaced at some point. It only addresses cases where a reference might be escaped through a single return value; it doesn't address escaping through 'out' parameters, or through a returned tuple.

- It fails to enable useful features like the swap function, or storing a scoped value in a container (well, outside of @trusted code, but that's beside the point).

- Because it isn't an integral part of the type system, but more of an external addition, it has a ton of special cases and little gotcha's when you try to do something complex with it. (ref parameters can't be scope, can't have pointers on scope values, which means you can't pass any kind of scope value by reference, you can't have scope types as template parameters, etc)

The two last ones feel like the most important problems to me. If all you want to do is variants of the identity function, and returning references to attributes, then return ref and return scope is everything you need (arguably). If you want to store containers of scoped values, swap scope values, and generally treat scope as a first-class citizen, then return scope and return ref seem like a step in the wrong direction.

The meta problem people seem to have with 'return scope' seems more of a social problem. Apparently a lot of people feel like you haven't treated their concerns seriously; part of it is that as far as I'm aware there hasn't been a proper, open brainstorming on how to address lifetime analysis in D.

My reading of the situation, which may be completely off-base, is that you took inspiration from Marc Schütz's proposal, and wrote something simpler, easier to understand and to code with, and following the model you developed when coming up with inout (no templates, KISS, don't use up too much language complexity estate on an optional feature), then entered a cycle of gradually improving it, eventually making DIP-1000.

People who don't like the direction DIP-1000 goes towards are upset because they feel way too much effort is going towards refining an idea they don't agree with in the first place. To speak bluntly, I don't think you've addressed their concerns at all, and I hope you do so before 'scope return' is set in stone.

> So, do what numerous people have done numerous times already, to no great effect?

Please don't be hostile. When you have a communication problem, being passive-aggressive will only makes it worse.

On 1/28/2017 3:51 AM, deadalnix wrote:
> I did so repeatedly for years and never reached to you or Andrei, so I'm not
> sure how that's going to change anything but here you go.

By being specific.


> The root problem you are trying to solve is to be able to specify that what
> comes out of a function has a common property with what come in. In the case of
> inout, this property is the type qualifier, in the case of return/scope this is
> the lifetime.

Yup.


> Same problem, same solution, same fallout.

What problem?

On 1/28/2017 6:56 AM, Olivier FAURE wrote:
> For what it's worth, here are my problems with 'return scope':
>
> - As far as I can tell, it's not properly documented. The github page for
> DIP-1000 is apparently pending a rewrite, and I can't find a formal definition
> of 'return scope' anywhere (the D reference 'Functions' page only mentions
> 'return ref', and in passing).

Yes, the documentation could be much better, and will be. Like any battle plan doesn't survive the first day of warfare, actually implementing -dip1000 has forced several adjustments. I expect more adjustments will be necessary. One of the larger difficulties is getting code with -dip1000 and without -dip1000 to play together. The bug Dicebot mentioned above is one of those. But this is the sort of problem any such scheme will have to deal with.


> - I personally don't like using the return keyword as anything but an
> instruction; when I'm reading code, I can have a good feeling of the code's flow
> by just looking at the indentation, the if/while/for blocks, and the
> break/throw/return instructions. I'll be the first to admit it's kind of minor
> though.

There's got to be some added syntax somewhere. I'd love to do it as pure compiler magic. Amazingly, if the code is all templates, that seems to work (the compiler can infer 'return' and 'scope' as necessary there).


> - It's an obvious monkey patch,

All new features of D have to be worked in to existing features with minimal disruption. We're stuck with that reality.


> and it will clearly have to be replaced at some point.
> It only addresses cases where a reference might be escaped through a
> single return value; it doesn't address escaping through 'out' parameters,

Yes it does (the general case is storing a value into any data structure pointed to by an argument).


> or through a returned tuple.

Yes it does (it's as if the tuple elements were fields of a struct).

In general, the idea is to understand what happens with pointers and values. Then, to understand how X works, reduce X to its constituent pointers and values, and that's how X must work.

It's like in electronics you'll get nowhere trying to understand how an amplifier works without thoroughly understand how voltage, current, and resistance works. Understanding the amplifier is built up from that.


> - It fails to enable useful features like the swap function, or storing a scoped
> value in a container (well, outside of @trusted code, but that's beside the point).

There will be a need for @system code for some things, that is correct. That's also true of Rust, where cyclic data structures have to be marked as unsafe, and functions cannot access mutable global data.

Storing a non-trivial data structure in a container is done by hiding the pointers in it with 'private' and providing access via the appropriate member functions. Safely managing memory is done with ref counted objects or GC memory.

'scope return' and 'ref return' allow ref counting containers to return temporary references to their internal data.


> - Because it isn't an integral part of the type system, but more of an external
> addition, it has a ton of special cases and little gotcha's when you try to do
> something complex with it. (ref parameters can't be scope, can't have pointers
> on scope values, which means you can't pass any kind of scope value by
> reference, you can't have scope types as template parameters, etc)

D is a complex language. There are LOTs of ways pointers can be handed around. Maybe if we throw D away and start over there would be fewer special cases, but we have to work it into the existing semantics.

Yes, you cannot express things in D like a pointer to a scope pointer. Time will tell, but in real code I've seen very little need for such things - little enough that it can be handled with @system code.


> The two last ones feel like the most important problems to me. If all you want
> to do is variants of the identity function, and returning references to
> attributes, then return ref and return scope is everything you need (arguably).
> If you want to store containers of scoped values, swap scope values, and
> generally treat scope as a first-class citizen, then return scope and return ref
> seem like a step in the wrong direction.

Nobody has come up with a better plan. A Rust-like system would require users to not just add annotations, but redesign all their code and data structures. It's out of the question.


> The meta problem people seem to have with 'return scope' seems more of a social
> problem. Apparently a lot of people feel like you haven't treated their concerns
> seriously; part of it is that as far as I'm aware there hasn't been a proper,
> open brainstorming on how to address lifetime analysis in D.

There has been off and on for about 10 years. Little has come of it.

Then came -dip25, which addressed the return ref problem. It worked surprisingly well. There was some severe criticism of it last year as being unusable, but those turned out to be implementation bugs that were not difficult to resolve.

'return scope' is little more than extending 'return ref' to deal with values.


> My reading of the situation, which may be completely off-base, is that you took
> inspiration from Marc Schütz's proposal, and wrote something simpler, easier to
> understand and to code with, and following the model you developed when coming
> up with inout (no templates, KISS, don't use up too much language complexity
> estate on an optional feature), then entered a cycle of gradually improving it,
> eventually making DIP-1000.

A reasonable summary.


> People who don't like the direction DIP-1000 goes towards are upset because they
> feel way too much effort is going towards refining an idea they don't agree with
> in the first place. To speak bluntly, I don't think you've addressed their
> concerns at all, and I hope you do so before 'scope return' is set in stone.

It's fair if you don't agree with my rationale, but that isn't the same as not addressing them at all. I believe I have addressed the issues you brought up here. If you'd like further clarification, please ask.


>> So, do what numerous people have done numerous times already, to no great effect?
> Please don't be hostile. When you have a communication problem, being
> passive-aggressive will only makes it worse.

I didn't write that.