isDelegate

static assert(isDelegate!(void delegate()));
static assert(!isDelegate!(void function()));

static assert(!isDelegate!(() {}));

void func()
{
}
static void staticFunc()
{
}
interface I
{
    @property int prop();
}

static assert(!isDelegate!func);
static assert(!isDelegate!staticFunc);

auto functionPointer = &staticFunc;
auto dg = &func;

static assert(!isDelegate!functionPointer);
static assert(isDelegate!dg);

static assert(!isDelegate!(I.prop));