std.v2020.algorithm etc[ WAS: Is run.d going to be expand for runtime and the phobos library?]

[Andrei Alexandrescu]

On 6/20/20 2:34 PM, Johannes Loher wrote:
> On Saturday, 20 June 2020 at 13:07:41 UTC, Paul Backus wrote:
>> On Saturday, 20 June 2020 at 12:42:01 UTC, Stanislav Blinov wrote:
>>> On Saturday, 20 June 2020 at 10:43:41 UTC, Paul Backus wrote:
>>>
>>>> Also, switch from `void popFront()` to `typeof(this) rest`, so that 
>>>> we can have `const` and `immutable` ranges.
>>>
>>> *Switch* is probably too restrictive. For a given range a `popFront` 
>>> may be more efficient than a `range = range.rest`. Making `rest` a 
>>> valid range primitive though, and using where appropriate - that'd be 
>>> awesome.
>>
>> For non-forward ranges, there's no promise that the original range (or 
>> any copies of it) will remain valid after calling `rest`, so you can 
>> always implement `rest` like this:
>>
>>     auto rest() {
>>         this.popFront;
>>         return this;
>>     }
> 
> Can’t make it const then... also some ranges probably cannot bee const 
> by design, e.g. byLine etc.

That function would be a fallback. Ranges that are const would implement 
it as a primitive not expressible with popFront.

Consider:

immutable List(T) {
     private T payload;
     private List next;
     public List tail() { return next; }
     ...
}

You can't implement popFront for this structure.