cast(bool)array must be rewritten to cast(bool)array.length.

assert(!""); // currently fails
assert(![]); // currently passes
assert(![' '][1..1]);  // passes
assert(!" "[1..1]);    // fails

assert(a==b && (!a&&b||!b&&a)); // might fail more or less randomly for dynamic arrays a,b

The current behavior is that cast(bool)array is translated to cast(bool)array.ptr. This is likely a leftover from the times when dynamic arrays implicitly converted to their .ptr properties. It does not convey any useful semantics, yet it is invoked implicitly every time a dynamic array appears in a boolean evaluation context.

struct DynArray{
    size_t length;
    int* ptr;
    alias ptr this;
}
void main(){
    DynArray a;
    int[] b;
    writeln(cast(bool)a); // false
    writeln(cast(bool)b); // false

    a.ptr = new	int;
    writeln(cast(bool)a); // true

    *(cast(int**)&b+1) = new int; // "b.ptr = new int"
    writeln(cast(bool)b); // true
}