std.typecons.Tuple and tuples
bearophile
bearophileHUGS at lycos.com
Mon Aug 2 08:12:33 PDT 2010
I know that three ways to do something looks a bit too much, but I'd like a third way to build a std.typecons tuple: I like to give field names, but to omit their types:
import std.typecons: Tuple;
import std.string: split;
import std.metastrings: Format, toStringNow;
// from dlibs1
template SeriesGen1(string txt, string separator, int max, int min=0) {
static if (min > max)
const SeriesGen1 = "";
else static if (min == max)
const SeriesGen1 = Format!(txt, toStringNow!(max));
else
const SeriesGen1 = SeriesGen1!(txt, separator, max-1, min) ~ separator ~
Format!(txt, toStringNow!(max));
}
// from dlibs1
template SeriesGen2(string txt, string separator, int max, int min=0) {
static if (min > max)
const SeriesGen2 = "";
else static if (min == max)
const SeriesGen2 = Format!(txt, toStringNow!(max),
toStringNow!(max));
else
const SeriesGen2 = SeriesGen2!(txt, separator, max-1, min) ~ separator ~
Format!(txt, toStringNow!(max),
toStringNow!(max));
}
// not sure about the ref return value
// can this be named just "Tuple"?
ref auto Tuple_(string names, T...)(T args)
if (split(names).length == T.length) {
enum string[] fieldNames = split(names);
mixin("return Tuple!(" ~
SeriesGen2!("T[%s], fieldNames[%s]", ", ", T.length-1) ~
")(" ~
SeriesGen1!("args[%s]", ", ", T.length-1) ~
");"
);
}
// demo --------------------
import std.stdio: writeln;
ref auto sqr2(int a, float b) {
return Tuple_!q{x y}(a * a, b * b);
}
void main() {
///*
with(sqr2(10, 5.5F)) {
writeln(x, " ", y);
} // test.d(...): Error: sqr2(10,5.5F) is not an lvalue
//*/
auto xy = sqr2(10, 5.5F);
with(xy) {
writeln(x, " ", y);
}
with(Tuple!(int, "a", float, "b")(10, 5.5F)) {
writeln(a, " ", b);
}
}
Can this Tuple!() overload the std.typecons.Tuple? (I have tried to integrate it, but I have failed at my first quick attempt).
-------------
This is in std.file:
void getTimes(in char[] name, out d_time ftc, out d_time fta, out d_time ftm);
Introducing tuples more into Phobos it becomes:
Tuple!(d_time "ftc", d_time "fta", d_time "ftm") getTimes(in string name);
But then you have to use it for example like this:
void main() {
auto t3 = getTimes("filename");
with(t3) {
writeln(ftc, " ", fta, " ", ftm);
}
}
While adding a bit of syntax sugar to D it becomes:
void main() {
// note: "fc" != "ftc"
(d_time fc, d_time fa, d_time fm) = getTimes("filename");
}
That syntax sugar means something like:
void main() {
auto __temp1 = getTimes("filename");
d_time fc = __temp1.field[0];
d_time fa = __temp1.field[1];
d_time fm = __temp1.field[2];
}
I think that sugar doesn't clash with C syntax.
Bye,
bearophile
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