On Monday, 9 August 2021 at 02:47:40 UTC, Mathias LANG wrote:
On Sunday, 8 August 2021 at 18:36:02 UTC, vit wrote:
Hello, is there reason why elements of input range must be
copyable?
By design, not that I can think of. But it is assumed all over
the place, unfortunately. You can make your `front` method
return by `ref`, but you're still going to get bitten as soon
as you do any `std.algorithm`-based operation, as storage
classes are not inferred
(https://issues.dlang.org/show_bug.cgi?id=9423) and things get
passed by value to your delegates by default. The problem can
also show up when you `foreach` over a range
(https://issues.dlang.org/show_bug.cgi?id=15413). And finally,
`std.algorithm` need to support it.
So currently you'll have to jump through a lot of hops to get
it to work. It'll be much easier to use your own `map` & co to
get the job done for the time being. Hopefully at some point in
the near future that won't be needed anymore.
Look like I am not the first who has this problem:
https://issues.dlang.org/show_bug.cgi?id=14478
I copy part of `std.algorithm` I use and change `isInputRange` to:
```d
enum bool isInputRange(R) = true
&& is(typeof(R.init) == R)
///no change
&& is(ReturnType!((R r) => r.empty) == bool)
///no change
&& is(typeof((return ref R r) => (auto ref
x){}(r.front))) ///Before: , is(typeof((return ref R r) =>
r.front))
&& !is(ReturnType!((R r) => r.front) == void)
///no change
&& is(typeof((R r) => r.popFront));
///no change
