Re: Empty VS null array?

[ProgrammingGhost]

On Thursday, 17 October 2013 at 23:14:51 UTC, anonymous wrote:
On Thursday, 17 October 2013 at 22:50:22 UTC, ProgrammingGhost 
wrote:
How do I find out if null was passed in? As you can guess I 
wasn't happy with the current behavior.

Code:

        import std.stdio;

        void main() {

                fn([1,2]);
                fn(null);
                fn([]);
        }
        void fn(int[] v) {
                writeln("-");
                if(v==null)
                        writeln("Use default");
                foreach(e; v)
                        writeln(e);
        }

Output

        -
        1
        2
        -
        Use default
        -
        Use default

On Thursday, 17 October 2013 at 22:51:24 UTC, ProgrammingGhost 
wrote:
Sorry I misspoke. I meant to say empty array or not null 
passed in. The 3rd call to fn is what I didn't like.

null implicitly converts to []. You can't distinguish them in 
fn.

You could add an overload for typeof(null), but that only 
catches the literal null, probably not what you'd expect:

import std.stdio;
void fn(typeof(null) v) {
        writeln("-");
        writeln("Use default");
}
void fn(int[] v) {
        writeln("-");
        foreach(e; v)
                writeln(e);
}
void main() {
        fn([1,2]);
        fn(null);
        fn([]);
        int[] x = null;
        fn(x);
}
----
-
1
2
-
Use default
-
-

Overloads are acceptable. But that behavior is odd although I do 
understand its being passed as value. I guess I have to suck it 
up and hope this behavior doesn't give me problems.