This looks like a correct D2 program:


import std.string: split;
template Foo(alias items) {
    static if (items.length == 0)
        enum Foo = 1;
    else
        enum Foo = 2;
}
enum string[] items = split("");
static assert(Foo!(items) == 1);
void main() {}


But DMD v2.046 prints at compile-time:

test.d(3): Error: expression (null.length) == 0u is not constant or does not evaluate to a bool
test.d(9): Error: template instance test.Foo!(items) error instantiating
test.d(9): Error: static assert  (2 == 1) is false

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

To fix it you have to test for null too:


import std.string: split;
template Foo(alias items) {
    static if (items == null || items.length == 0)
        enum Foo = 1;
    else
        enum Foo = 2;
}
enum string[] items = split("");
static assert(Foo!(items) == 1);
void main() {}