Optional and NotNull version 0.5.0 - swift optional like and scala option like

[aliak]

On Friday, 17 August 2018 at 06:59:48 UTC, Petar Kirov 
[ZombineDev] wrote:
> On Thursday, 16 August 2018 at 18:10:38 UTC, jmh530 wrote:
>> On Thursday, 16 August 2018 at 12:25:14 UTC, aliak wrote:
>>> Hi
>>>
>>> See: https://optional.dub.pm
>>>
>>> I've totally revamped the Optional type and am now quite 
>>> happy with. It has a range interface and safe dispatching and 
>>> can be used to 1) avoid null dereferencing, 2) have non-null 
>>> guarantees, and 3) show clear intent where there may or may 
>>> not be a value. It's also @nogc and @safe and mutation of the 
>>> original object during safe dispatching works as well.
>>>
>>
>> The readme.md page looks great. You might mention that it 
>> works with @nogc and @safe (I presume Optional and NotNull).
>>
>> One question: Suppose there was a @weaksafe that has all the 
>> same features @safe except that it relaxed the requirement of 
>> "No taking the address of a local variable or function 
>> parameter." so that you could take the address of a NotNull 
>> variable. Are there any reasons why this would be unsafe? I 
>> imagine NotNull requires some type of run-time checking, but 
>> other than that I don't see why not.
>
> Actually "@weaksafe" already exists in the form of `@safe` + 
> `-dip1000` - you can take the address of a local variable in 
> `@safe` code and then you get a `scope`-ed pointer, which 
> you're not allowed to escape.

Right! There's that. That would most certainly help here.

So the first non-safety part of Optional comes from the dispatch 
function. To support mutations, the pattern is basically:

struct Optional(T) {
   T value;
   auto dispatch() inout {
     return inout Dispatcher(&this);
   }
}

Now the thing is, the Dispatcher type is actually disabled on 
copying, construction and identity assignment. So I wonder if 
this can be marked @trusted in theory. Since the address never 
escapes from a Dispatcher object.

And the other part is when two addresses are compared (which is 
local only): 
https://github.com/aliak00/optional/blob/83edfef7130ec02992ec2986611718f80167234d/source/optional/dispatcher.d#L42