On Sunday, 5 May 2019 at 18:53:08 UTC, Russel Winder wrote:
Hi,
I had merrily asumed I could implement nth Fibonacci number
with:
takeOne(drop(recurrence!((a, n) => a[n-1] + a[n-2])(zero,
one), n)).front
where zero and one are of type BigInt, and n is of type size_t.
However both dmd and ldc2 complain saying:
[…]
I am now at the WTF stage – how can I show this example on
Thursday in my DevoxxUK presentation?
I am close to giving up and imbibing of too much Pernod.
`recurrence` takes the `CommonType` of the initial values and
declares its internal state as an array of this type, however
when at least one of the values is const or immutable, the
`CommonType` is const too, or even immutable in the case when all
values are immutable.
The state being const/immutable means that the following step,
initializing it, can't work, since, well, the array cannot be
modified (hence the errors).
I'd say this can be considered to be a bug with `recurrence`.
You can solve this issue by constructing and passing mutable
versions of `one` and `zero` to `recurrence`.
