2022-03-09 03:08:15 -06:00
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# Convert by `as`
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2022-03-09 02:34:49 -06:00
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Rust provides no implicit type conversion(coercion) between primitive types. But explicit type conversions can be performed using the `as` keyword.
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1. π
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```rust,editable
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// FIX the errors and FILL in the blank
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// DON'T remove any code
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fn main() {
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let decimal = 97.123_f32;
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let integer: __ = decimal as u8;
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let c1: char = decimal as char;
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let c2 = integer as char;
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assert_eq!(integer, 'b' as u8);
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println!("Success!")
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}
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```
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2. ππ By default, overflow will cause compile errors, but we can add an global annotation to suppress these errors.
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```rust,editable
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fn main() {
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assert_eq!(u8::MAX, 255);
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// the max of `u8` is 255 as shown above.
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// so the below code will cause an overflow error: literal out of range for `u8`.
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// PLEASE looking for clues within compile errors to FIX it.
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// DON'T modify any code in main.
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let v = 1000 as u8;
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println!("Success!")
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}
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```
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3. ππ when casting any value to an unsigned type `T`, `T::MAX + 1` is added or subtracted until the value fits into the new type.
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```rust,editable
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fn main() {
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assert_eq!(1000 as u16, __);
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assert_eq!(1000 as u8, __);
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// For positive numbers, this is the same as the modulus
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println!("1000 mod 256 is : {}", 1000 % 256);
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assert_eq!(-1_i8 as u8, __);
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// Since Rust 1.45, the `as` keyword performs a *saturating cast*
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// when casting from float to int. If the floating point value exceeds
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// the upper bound or is less than the lower bound, the returned value
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// will be equal to the bound crossed.
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assert_eq!(300.1_f32 as u8, __);
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assert_eq!(-100.1_f32 as u8, __);
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// This behavior incurs a small runtime cost and can be avoided
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// with unsafe methods, however the results might overflow and
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// return **unsound values**. Use these methods wisely:
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unsafe {
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// 300.0 is 44
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println!("300.0 is {}", 300.0_f32.to_int_unchecked::<u8>());
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// -100.0 as u8 is 156
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println!("-100.0 as u8 is {}", (-100.0_f32).to_int_unchecked::<u8>());
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// nan as u8 is 0
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println!("nan as u8 is {}", f32::NAN.to_int_unchecked::<u8>());
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}
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}
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```
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4. πππ Raw pointer can be converted to memory address (integer) and vice versa
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```rust,editable
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// FILL in the blanks
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fn main() {
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let mut values: [i32; 2] = [1, 2];
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let p1: *mut i32 = values.as_mut_ptr();
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let first_address: usize = p1 __;
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let second_address = first_address + 4; // 4 == std::mem::size_of::<i32>()
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let p2: *mut i32 = second_address __; // p2 points to the 2nd element in values
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unsafe {
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// add one to the second element
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__
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}
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assert_eq!(values[1], 3);
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println!("Success!")
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}
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```
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2022-03-09 03:08:15 -06:00
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5. πππ
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2022-03-09 02:34:49 -06:00
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```rust,editable
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fn main() {
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let arr :[u64; 13] = [0; 13];
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assert_eq!(std::mem::size_of_val(&arr), 8 * 13);
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let a: *const [u64] = &arr;
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let b = a as *const [u8];
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unsafe {
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assert_eq!(std::mem::size_of_val(&*b), __)
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}
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2022-03-09 21:05:18 -06:00
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println!("Success!")
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2022-03-09 02:34:49 -06:00
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}
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```
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