std.typecons.nullable and nullableRef functions

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2013-03-02T13:37:47Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=9637

Description

Spinoff of Issue 9265

I suggest to add to std.typecons two small functions that help the creation of a Nullable and NullableRef:


import std.typecons;
void main() {
    int x;
    auto n1 = Nullable!int(x);
    auto n2 = NullableRef!int(&x);
    auto n3 = nullable(x); // missing
    auto n4 = nullableRef(&x); // missing
}


This gets handy when the type of the item is complex:

auto n = nullable(data);

Instead of:

auto n = Nullable!(immutable int[4])(data);

- - - - - - - - - - - -

Note: maybe it's possible to support Nullable(T, T nullValue) like this:

auto n5 = nullable!(int.max)(x);

But maybe for simplicity it's better to not support this.