rust-by-practice/en/src/type-conversions/as.md

Convert by as

Rust provides no implicit type conversion(coercion) between primitive types. But explicit type conversions can be performed using the as keyword.

1. 🌟

// FIX the errors and FILL in the blank
// DON'T remove any code
fn main() {
    let decimal = 97.123_f32;

    let integer: __ = decimal as u8;

    let c1: char = decimal as char;
    let c2 = integer as char;

    assert_eq!(integer, 'b' as u8);

    println!("Success!")
}

2. 🌟🌟 By default, overflow will cause compile errors, but we can add an global annotation to suppress these errors.

fn main() {
    assert_eq!(u8::MAX, 255);
    // the max of `u8` is 255 as shown above.
    // so the below code will cause an overflow error: literal out of range for `u8`.
    // PLEASE looking for clues within compile errors to FIX it.
    // DON'T modify any code in main.
    let v = 1000 as u8;

    println!("Success!")
}

3. 🌟🌟 when casting any value to an unsigned type T, T::MAX + 1 is added or subtracted until the value fits into the new type.

fn main() {
    assert_eq!(1000 as u16, __);

    assert_eq!(1000 as u8, __);

    // For positive numbers, this is the same as the modulus
    println!("1000 mod 256 is : {}", 1000 % 256);

    assert_eq!(-1_i8 as u8, __);
    
    // Since Rust 1.45, the `as` keyword performs a *saturating cast* 
    // when casting from float to int. If the floating point value exceeds 
    // the upper bound or is less than the lower bound, the returned value 
    // will be equal to the bound crossed.
    assert_eq!(300.1_f32 as u8, __);
    assert_eq!(-100.1_f32 as u8, __);
    

    // This behavior incurs a small runtime cost and can be avoided 
    // with unsafe methods, however the results might overflow and 
    // return **unsound values**. Use these methods wisely:
    unsafe {
        // 300.0 is 44
        println!("300.0 is {}", 300.0_f32.to_int_unchecked::<u8>());
        // -100.0 as u8 is 156
        println!("-100.0 as u8 is {}", (-100.0_f32).to_int_unchecked::<u8>());
        // nan as u8 is 0
        println!("nan as u8 is {}", f32::NAN.to_int_unchecked::<u8>());
    }
}

4. 🌟🌟🌟 Raw pointer can be converted to memory address (integer) and vice versa

// FILL in the blanks
fn main() {
    let mut values: [i32; 2] = [1, 2];
    let p1: *mut i32 = values.as_mut_ptr();
    let first_address: usize = p1 __; 
    let second_address = first_address + 4; // 4 == std::mem::size_of::<i32>()
    let p2: *mut i32 = second_address __; // p2 points to the 2nd element in values
    unsafe {
        // add one to the second element
        __
    }
    
    assert_eq!(values[1], 3);

    println!("Success!")
}

5. 🌟🌟🌟

fn main() {
    let arr :[u64; 13] = [0; 13];
    assert_eq!(std::mem::size_of_val(&arr), 8 * 13);
    let a: *const [u64] = &arr;
    let b = a as *const [u8];
    unsafe {
        assert_eq!(std::mem::size_of_val(&*b), __)
    }

    println!("Success!")
}