On 4/2/18 5:31 AM, Timoses wrote:
On Sunday, 1 April 2018 at 15:54:16 UTC, Steven Schveighoffer wrote:
I currently have a situation where I want to have a function that
accepts a parameter optionally.
I thought maybe Nullable!int might work:
void foo(Nullable!int) {}
void main()
{
foo(1); // error
int x;
foo(x); // error
}
Can somebody enlighten me what this topic is about?
I thought an optional parameter would be as easy as
void foo(int i = 0) { writeln(i); }
void main()
{
int x;
foo(x);
foo(1);
foo();
}
Is the Nullable!int approach because 'i' would always "optionally" be 0
if not passed with above 'foo'?
I'm talking about optionals as they are in other languages, such as
Swift: https://en.wikipedia.org/wiki/Option_type
In other words, there is a distinct state of "not provided" from the
other values it might take.
Nullable works to fill this purpose, but I didn't realize that I'd have
to wrap all calls to it. I was hoping for something more like Swift's
option types. In Swift, I would do:
function foo(x: Int?)
And I can check x to see if it's nil inside the function. I can just
call foo with a plain Int and it works fine. Int implicitly casts to
Int?, but Int? needs an explicit conversion to Int. That was the
relationship I was looking for. Apparently, not attainable in D, unless
you do it on initialization.
-Steve
