range algorithms on container class

[Alex Burton]

On Thursday, 9 January 2020 at 10:26:07 UTC, Jonathan M Davis 
wrote:
> On Wednesday, January 8, 2020 10:56:20 PM MST rikki cattermole 
> via Digitalmars-d-learn wrote:
>> Slicing via the opSlice operator overload is a convention, not 
>> a requirement.
>
> It's not a requirement, but it's more than a convention. If you 
> use the container with foreach, the compiler will call opSlice 
> on the container to get a range. So, there's no need to 
> implement opApply to iterate over a container with foreach. You 
> could choose to implement a container with opApply and use a 
> function other than opSlice for getting a range, but the 
> compiler understands enough to try to slice the container for 
> you automatically when using it with foreach.
>
> - Jonathan M Davis

Implementing opApply allowed me to use foreach on the container.

I would expect that returning a slice would not be logically 
possible for many container types. A slice cannot be a range 
either, otherwise you would need to call the array algorithm to 
assign a slice of an array to another array.

So the compiler must be creating a forward iterating range to 
pass into the range algorithms in these cases.

That foreach, and range algorithms can work on a native array but 
only foreach can work on custom container type looks like a gap 
in the language.