Be warned there's a nasty bug here:
This works:
typedef fun pred (T:TYPE):TYPE => typematch T with
| 7 => 6
| 6 => 5
| 5 => 4
| 4 => 3
| 3 => 2
| 2 => 1
| 1 => 0
endmatch;
class Trick2[T] {
virtual fun rank : 1 -> int;
}
instance [N] Trick2[N] {
fun rank() => memcount[N].int + Trick2[pred N]::rank ();
}
instance Trick2 [1] {
fun rank() => 1;
}
println$ "by instance " + str #Trick2[4]::rank;
however this doesn't:
fun rank() => memcount[N] + Trick2[pred N]::rank ();
The error message is misleading:
/felix>flx --test=build/release rank
Flx_egen: Waring: delayed virtual instantiation, external fun rank<30953>
CLIENT ERROR
Instantiate virtual function(2) rank<30953>, no instance for ts=4
Instances are unit->unit
In /Users/johnskaller/felix/build/release/lib/std/io/textio.flx: line 138, cols
76 to 71
137: proc writeln : ostream * string ="::flx::rtl::ioutil::writeln($1,$2);";
138: proc write : ostream * string ="::flx::rtl::ioutil::write($1,$2);";
*
139: proc write : ostream * utiny ="$1->put($2);";
See also /Users/johnskaller/felix/./rank.flx: line 45, cols 18 to 30
44: class Trick2[T] {
45: virtual fun rank : 1 -> int;
*************
46: }
In fact, memcount[] is of type size, which can be added to an int
to give type size, so the rank() function returns type size,
therefore it isn't an "override" or instance of the virtual rank.
I personally didn't realise the whole type had to match,
not just the signature: I'd have expected if the signature
matched and the return type didn't I get a binding error.
So be warned. This is not a bug, but it is misleading.
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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