On Monday, 17 July 2017 at 12:38:27 UTC, Steven Schveighoffer wrote:
On 7/16/17 1:04 PM, Andrei Alexandrescu wrote:
On 7/16/17 9:10 AM, Mike Parker wrote:
Congratulations to Timon Gehr. Not only was his "Static foreach" DIP accepted, it picked up a good deal of praise from Walter & Andrei.

Indeed. Kudos to Timon (and thanks Mike for driving the process). This is a well done DIP that many others could draw inspiration from. -- Andrei

What is the resolution of how break statements affect static foreach/foreach?

i.e. this section:

"As some consider this to be potentially confusing, it has been suggested that break and continue directly inside static foreach should instead be compiler errors and require explicit labels. This DIP leaves this decision to the language authors, but recommends the above semantics."


I think the only reliable way is to not use jumps (goto, break, continue) at all.
E.g. if you want to unroll the following loop:

foreach (x; someRange)
    if (x.isSpecial)


You would need to guard every statement/declaration:

static foreach (x; someRange)
    static if (!x.isSpecial)

Hence why, I believe that we need more powerful range-like algorithms for manipulating alias sequences. Though in case this using what's in std.meta is not much of a stretch, ultimately it becomes repetitive and very verbose when used more heavily and ultimately doesn't offer significant improvement over the code above:

foreach (x; Filter!(templateNot!isSpecial, aliasSeqOf!someRange))

(I'm working on a functional programming library which would allow to use the same functions to transform ranges, alias sequences and other reducible/iterable objects, which should make composing alias sequence transformations a bit more easy and scalable.)

Anyway, if you're iterating over homogeneous expression sequences, via DIP1010 you should be able to use std.algorithm and std.range functions directly, since the resulting range would be automatically evaluated at CT and expanded as an expression sequence:

static foreach (x; someRange.filter!(x => !x.isSpecial))

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