The function in question is std.algorithm.searching's until [1].

Here are the definitions:

Until!(pred, Range, Sentinel)
until(alias pred = "a == b", Range, Sentinel)
(Range range, Sentinel sentinel, OpenRight openRight = OpenRight.yes)
if (!is(Sentinel == OpenRight));


Until!(pred, Range, void)
until(alias pred, Range)
(Range range, OpenRight openRight = OpenRight.yes);

Now the first thing that came to mind was that it seemed odd to have openRight be a runtime flag instead of a compile-time flag. But that didn't hinder my usage of it, so I went ahead and called the function like so:

range.until!(e => e > f)(No.openRight)

and I got an error saying the function could not be deduced, so I went looking in the source code and found:

enum OpenRight

But I had assumed OpenRight was an alias for a Flag type [2], so I had called it wrong.

Does anyone have any idea why the function is defined this way?

1. Why is openRight a runtime flag? Is there really a use case for this?

2. Why is openRight not a Flag type?

here is the definition I was expecting:

alias OpenRight = Flag!"openRight";

auto until(alias pred = "a == b", OpenRight openRight = Yes.openRight, Range, Sentinel)
(Range range, Sentinel sentinel);

auto until(alias pred, OpenRight openRight = Yes.openRight)(Range range);


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