On 1/9/11 1:12 PM, Daniel Gibson wrote:
Am 09.01.2011 19:48, schrieb Robert M. Münch:
On 2011-01-09 19:42:22 +0100, Andrei Alexandrescu said:
I wrote a simple helper, in spirit with some recent discussions:
Hi, EITHER normaly means: This or that, so it's more like an IF/ELSE.
How about ANY? IMO
1==any(1, 2, 3)
describes pretty good what is meant.
I agree.
Problem with any/either is that it encodes the comparison inside the
data. You can do == and !=, but algorithms want to work with general
predicates, and any can't work with arbitrary predicates - unless the
predicates themselves are designed to work with it.
For now I added this to std.algorithm:
/**
Consume all elements from $(D r) that are equal to one of the elements
$(D es).
*/
void skipAll(alias pred = "a == b", R, Es...)(ref R r, Es es)
{
loop:
for (; !r.empty; r.popFront())
{
foreach (i, E; Es)
{
if (binaryFun!pred(r.front, es[i]))
{
continue loop;
}
}
break;
}
}
unittest
{
auto s1 = "Hello world";
skipAll(s1, 'H', 'e');
assert(s1 == "llo world");
}
I wonder if it's worthwhile encoding the predicate inside the compared
elements. In that case, any would return a type that also has the
predicate. Something like this:
struct Any(alias pred = "a == b", Es...) { ... }
Then you'd put the predicate by the call to any, not by the call to the
algorithm:
skipAll(r, any!"a > b"(x, y, z));
Then skipAll doesn't need to worry about the predicate - it just uses ==
and !=.
If this paradigm has a landslide advantage over the current structure,
we'd need to rewrite a lot of std.algorithm.
Andrei
