On Sunday, 25 October 2015 at 05:45:15 UTC, Nerve wrote:
On Sunday, 25 October 2015 at 05:05:47 UTC, Rikki Cattermole
wrote:
Since I have no idea what the difference between Some(_), None
and default. I'll assume it's already doable.
_ represents all existing values not matched. In this case,
Some(_) represents any integer value that is not 7. None
specifically matches the case where no value has been returned.
We are, in most languages, also able to unwrap the value:
match x {
Some(7) => "Lucky number 7!",
Some(n) => "Not a lucky number: " ~ n,
None => "No value found"
}
Or something to that effect. The equivalent switch statement
right now would be:
if (x.hasValue()) {
switch (*x.peek!(int)) {
case 7: writeln("Lucky number seven!"); break;
default: writeln("Not a lucky number: ",
*x.peek!(int)); break;
}
} else {
writeln("No value.");
}
This does not return a value (is a procedural structure); the
switch cannot match null; in order to unwrap, we must call
peek() again; and between the extra if-else and the break
statements, this is not as clean.
As a note, pattern matching could almost be considered an
extended form of the ?: operator, which matches over value
cases rather than boolean truthiness.
Apologies if this is all below you, I'm not in Andrei's or
Walter's league, just an interested party trying to make
suggestions to better the language.
Although it doesn't exactly fit the problem at hand I'd like to
mention
predSwitch. For most cases it does what you could expect from
pattern
matching I think. Here is an example showing its strength and
limits on your
showcase:
import std.conv;
import std.stdio;
import std.algorithm.comparison;
import std.variant;
void main(string[] args) {
Variant x;
x = 42;
if (x.hasValue) {
x.predSwitch!((a,b) => *a.peek!int == b) (
7, "Lucky number!",
42, "This should be a lucky number too!",
"No luck, the number was " ~ x.to!string
).writeln;
}
else {
writeln("No value");
}
}
