On 1/22/15 11:41 AM, Russel Winder via Digitalmars-d-learn wrote:
Playing with factorial implementations, as you do. I had a D
implementation using ulong. Not sensible obviously since overflow is a
bit of a problem. But the code worked, as did the tests. Now converting
to BigInt and…
The standard explicit iteration form uses a loop:
for(i; 2..n+1)
for n = 0 or 1 this loop doesn't loop since the range is [,). However
for BigInt:
for(i; two..n + one)
the loop starts at 0 and just keeps on going. This is clearly not good.
Am I having a mental breakdown or is this a real bug?
The issue:
import std.stdio;
struct S
{
int x;
int opCmp(const S other) const { writeln("compare"); return x <
other.x ? -1 : x > other.x ? 1 : 0;}
bool opEquals(const S other) const { writeln("equals"); return x ==
other.x;}
ref S opOpAssign(string op)(int other)
{
mixin("x " ~ op ~ "= other;");
return this;
}
}
void main()
{
immutable S one = S(1);
immutable S two = S(2);
foreach(s; one..two) {}
}
output:
equals
equals
So foreach(S; one..two) translates to:
for(S x = one; x != two; x += 1)
which explains the infinite loop. I'm almost positive foreach(x; 1..2)
uses comparison instead of equality to check for end condition.
-Steve
