On Sunday, 25 October 2015 at 06:22:51 UTC, TheFlyingFiddle wrote:
You can do something very similar to that. With slightly
different syntax.
import std.traits;
import std.conv;
import std.variant;
struct CMatch(T...) if(T.length == 1)
{
alias U = typeof(T[0]);
static bool match(Variant v)
{
if(auto p = v.peek!U)
return *p == T[0];
return false;
}
}
auto ref match(Handlers...)(Variant v)
{
foreach(handler; Handlers)
{
alias P = Parameters!handler;
static if(P.length == 1)
{
static if(isInstanceOf!(CMatch, P[0]))
{
if(P[0].match(v))
return handler(P[0].init);
}
else
{
if(auto p = v.peek!(P[0]))
return handler(*p);
}
}
else
{
return handler();
}
}
assert(false, "No matching pattern");
}
unittest
{
Variant v = 5;
string s = v.match!(
(CMatch!7) => "Lucky number seven",
(int n) => "Not a lucky number: " ~ n.to!string,
() => "No value found!");
writeln(s);
}
That is actually freaking incredible. It evaluates to a value,
unwraps values, matches against the None case...I guess the only
thing it doesn't do is have compiler-enforced matching on all
cases. Unless I'm just slow this morning and not thinking of
other features a pattern match should have.
