On Mon, 08 Aug 2011 16:50:48 -0400, Philippe Sigaud
<[email protected]> wrote:
On Mon, Aug 8, 2011 at 21:55, Steven Schveighoffer <[email protected]>
wrote:
You still can do it, but you have to do it by still using compile-time
constants as indexes:
auto x = 1;
Tuple!(int, short) a;
a[0] = 1;
switch(x)
{
case 0:
a[0] = 2;
break;
case 1:
a[1] = 2;
break;
default:
assert(0, "does not compute!");
}
Christian, I think Steven even suggested in an article some months ago
that this big switch could be generated at compile time.
Steven, do you have a link somewhere?
Sorry, wasn't me...
I mean, the tuple length is known as C-T. It's easy to loop on it and
build a string of cases. If you wrap it in a function, it becomes a
runtime switcher.
Proof of concept:
import std.typecons;
string generateSwitches(T...)()
{
string result = "switch(x) {\n";
foreach(i,Type; T)
{
result ~= "case " ~ to!string(i) ~ ":\n"
~ "fun(tup[" ~ to!string(i) ~ "]);\n"
~ "break;\n";
}
return result ~ "default:\n"
~ "assert(0, q{Bad index: } ~ to!string(x));\n}";
}
void actOnTuple(alias fun, T...)(int x, ref Tuple!T tup)
{
mixin(generateSwitches!(T));
}
void foo(T)(ref T t) { writeln(t); t = T.init;}
void main()
{
auto tup = tuple(1, 3.14, "abc");
auto x = 1;
actOnTuple!foo(x, tup);
writeln(tup);
}
I like this idea. I think it belongs in phobos somewhere, if not already.
-Steve
