On Saturday, 27 February 2016 at 04:31:03 UTC, Mint wrote:
So, I noticed that one way I frequently use the chain function
defined std.range is as sort of an else-clause.
ie.
return elements
.map!( . . . )
.filter!( . . . )
.chain(fallback.only)
.front;
After transforming and filtering elements, chain would
effectively append a fallback element to the resulting range,
and then the first element would be taken. Hence if the result
of filter (or the initial range) was empty, the result would be
fallback.
My concern is that in some cases my fallback is expensive to
compute, and acts as a performance sink.
I'm wondering if about the possibility of having a similar
function that took a range as a lazy parameter. Specifically, a
the parameter would not be evaluated unless one of the
resulting range's functions were called. Thoughts?
With std.typecons.Option[1] it becomes:
return elements
.map!(…)
.filter!(…)
.frontOption
.getOrElse(fallback);
`fallback` is a lazy argument.
[1] https://github.com/D-Programming-Language/phobos/pull/3915
