1.
```rust
struct A;          // Concrete type `A`.
struct S(A);       // Concrete type `S`.
struct SGen<T>(T); // Generic type `SGen`.

fn reg_fn(_s: S) {}

fn gen_spec_t(_s: SGen<A>) {}

fn gen_spec_i32(_s: SGen<i32>) {}

fn generic<T>(_s: SGen<T>) {}

fn main() {
    // Using the non-generic functions
    reg_fn(S(A));          // Concrete type.
    gen_spec_t(SGen(A));   // Implicitly specified type parameter `A`.
    gen_spec_i32(SGen(6)); // Implicitly specified type parameter `i32`.

    // Explicitly specified type parameter `char` to `generic()`.
    generic::<char>(SGen('a'));

    // Implicitly specified type parameter `char` to `generic()`.
    generic(SGen('c'));
}
```

2.
```rust
fn sum<T:std::ops::Add<Output = T>>(x: T, y: T) -> T {
    x + y
}

fn main() {
    assert_eq!(5, sum(2i8, 3i8));
    assert_eq!(50, sum(20, 30));
    assert_eq!(2.46, sum(1.23, 1.23));
}
```


3.
```rust
struct Point<T> {
    x: T,
    y: T,
}

fn main() {
    let integer = Point { x: 5, y: 10 };
    let float = Point { x: 1.0, y: 4.0 };
}
```

4.
```rust
// modify this struct to make the code work
struct Point<T, U> {
    x: T,
    y: U,
}

fn main() {
    // DON'T modify here
    let p = Point{x: 5, y : "hello".to_string()};
}
```

5.
```rust
struct Val<T> {
    val: T,
}

impl<T> Val<T> {
    fn value(&self) -> &T {
        &self.val
    }
}


fn main() {
    let x = Val{ val: 3.0 };
    let y = Val{ val: "hello".to_string()};
    println!("{}, {}", x.value(), y.value());
}
```