isNullSettable

class C {}
struct S1 {
    void opAssign(int*) {}
}
static assert(isNullSettable!S1);
static assert(isNullSettable!C);
static assert(isNullSettable!(int*));

struct S2 {}
static assert(!isNullSettable!S2);
static assert(!isNullSettable!int);

struct S3 {
    @disable this();
    void opAssign(int*) {}
}
static assert(isNullSettable!S3);