foreach range with index

[Luís Marques via Digitalmars-d]

On Wednesday, 14 June 2017 at 16:17:50 UTC, Steven Schveighoffer 
wrote:
> I think opApply is kind of a forgotten piece of the language 
> since ranges have been introduced. We could resurrect it quite 
> easily this way, as opApply with template parameters that 
> return another range does not conflict with opApply that takes 
> a delegate. Easy to see if one works and if not try something 
> else. The huge benefit of this mechanism is to allow complete 
> control to the type over how it should be iterated, and not 
> have to fight the compiler.

You say "quite easily". I'm afraid this will linger. Please let's 
not drop the ball on this, whatever the chosen solution is.

> This is inherent of arrays working differently than ranges, but 
> being considered ranges via std.array. People consider slices 
> to be ranges, but they really aren't as far as the compiler is 
> concerned.

Sorry, I'm not seeing the connection. foreach is an abstract 
iteration statement and we are just discussion if it is 
reasonable for foreach to keep track of the iteration number.

> I don't know if there is room to allow range-defined indexes 
> and foreach-defined indexes. foreach(a, b; someRange) has to do 
> one or the other. Otherwise, changes to how someRange operates 
> can make this a completely different operation.

Seems like exactly what we want. If you add a customization to 
someRange to change the iteration behavior then each relevant 
foreach automatically switches from the default to the requested 
behavior. That's exactly the point of programming to abstract 
interfaces.