On Wednesday, 12 April 2023 at 13:09:07 UTC, Ali Çehreli wrote:
Not every type is null'able but nullable. ;) So, a design may
use the following:
https://dlang.org/library/std/typecons/nullable.html
I implemented Handler into the Voldermort build, which Walter
loved so much. For convenience, I put an alias between the
template and the function. But Nullable didn't work, instead
it's returning T.init...
```d
template Handler(alias A)
{
alias T = typeof(A);
auto Handler()
{
struct Impl
{
T*[string] data;
void set(string key, ref T value)
{
data[key] = &value;
}
auto opIndex(string key)
{
if (auto ret = key in data)
{
return **ret;
}
return T.init;/*
import std.typecons : Nullable;
return Nullable!T.init;//*/
}
auto opSlice()
{
T[] result;
foreach (ref value; data.values)
result ~= *value;
return result;
}
}
return Impl();
}
}
import std.stdio;
void main()
{
struct List { string product; float price; }
auto fruits = [ List("Manderin", 3.79),
List("Orange", 2.99),
List("Kiwi", 0.59),
];
auto handlers = Handler!fruits;
handlers.set("fruits", fruits);
// please try it: ^------v
foreach(h; handlers["fruit"])
{
h.product.write(": ");
h.price.writeln(" €");
}
auto handler = Handler!(List());
import std.conv : text;
foreach(i, ref fruit; fruits)
{
handler.set(i.text, fruit);
}
handler[].writeln;
} /* Prints:
Manderin: 3.79 €
Orange: 2.99 €
Kiwi: 0.59 €
[List("Kiwi", 0.59), List("Manderin", 3.79), List("Orange",
2.99)]
*/
```
SDB@79
