On Tuesday, 20 May 2014 at 20:15:09 UTC, Dominikus Dittes Scherkl
wrote:
/// create a fixed size array with the given name and with
*max* entries
max + 1 entries
/// of immutable values of the same type as the return value of
the
/// given function.
/// it contains the values of that function in the range
[0..max].
string makeLookupTable(alias fn, uint max=255)(string name)
pure @safe if(is(typeof(fn(max))))
{
string table = "immutable " ~ to!string(typeof(fn(max))) ~
"[" ~ to!string(max+1) ~ "] " ~ name ~"= [ ";
foreach(i; 0..max) table ~= to!string(fn(i) ~ ", ";
return table ~ to!string(fn(max) ~" ]";
}
Couldn't resist purging that of the string fiddling:
private template staticIota(uint n)
{
import std.typetuple: TypeTuple;
static if(n == 0) alias staticIota = TypeTuple!();
else alias staticIota = TypeTuple!(.staticIota!(n - 1), n -
1);
}
template lookupTable(alias fn, uint max = 255)
{
import std.traits: ReturnType;
import std.typetuple: staticMap;
static assert(max < uint.max);
enum length = max + 1;
enum ctfn(uint x) = fn(x);
alias elements = staticMap!(ctfn, staticIota!length);
enum ReturnType!fn[length] lookupTable = [elements];
}
void main()
{
char f(uint x) pure @safe {return x == 42 ? '!' : '.';}
static immutable t = lookupTable!f;
static assert(is(typeof(t) == immutable char[256]));
assert(t[42] == '!');
}
