Compiler/Phobos/Types problem — panic level due to timing.

[Russel Winder]

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:

/usr/include/dmd/phobos/std/range/package.d(5770): Error: template std.bigint.BigInt.opAssign cannot deduce function from argument types !()(immutable(BigInt)) immutable, candidates are:
/usr/include/dmd/phobos/std/bigint.d(178):        std.bigint.BigInt.opAssign(T)(T x) if (isIntegral!T)
/usr/include/dmd/phobos/std/bigint.d(194):        std.bigint.BigInt.opAssign(T : BigInt)(T x)
/usr/include/dmd/phobos/std/range/package.d(5770): Error: template std.bigint.BigInt.opAssign cannot deduce function from argument types !()(immutable(BigInt)) immutable, candidates are:
/usr/include/dmd/phobos/std/bigint.d(178):        std.bigint.BigInt.opAssign(T)(T x) if (isIntegral!T)
/usr/include/dmd/phobos/std/bigint.d(194):        std.bigint.BigInt.opAssign(T : BigInt)(T x)
fibonacci.d(25): Error: template instance `fibonacci.declarative.recurrence!((a, n) => a[n - 1] + a[n - 2], immutable(BigInt), immutable(BigInt))` error instantiating
/usr/include/dmd/phobos/std/range/package.d(5720): Error: template std.bigint.BigInt.opAssign cannot deduce function from argument types !()(immutable(BigInt)) immutable, candidates are:
/usr/include/dmd/phobos/std/bigint.d(178):        std.bigint.BigInt.opAssign(T)(T x) if (isIntegral!T)
/usr/include/dmd/phobos/std/bigint.d(194):        std.bigint.BigInt.opAssign(T : BigInt)(T x)
/usr/include/dmd/phobos/std/range/package.d(3177): Error: template instance `std.range.primitives.isInputRange!(Recurrence!(__lambda2, immutable(BigInt), 2LU))` error instantiating
fibonacci.d(25): Error: template std.range.drop cannot deduce function from argument types !()(Recurrence!(__lambda2, immutable(BigInt), 2LU), immutable(ulong)), candidates are:
/usr/include/dmd/phobos/std/range/package.d(3176):        std.range.drop(R)(R range, size_t n) if (isInputRange!R)

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.

-- 
Russel.
===========================================
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: This is a digitally signed message part
URL: <http://lists.puremagic.com/pipermail/digitalmars-d-learn/attachments/20190505/aa6e7cd8/attachment.sig>