Rust提供原始类型到隐式类型之间的转换(强制)。但是，显式类型转换可以使用关键字as进行。
整数类型之间的转换规则遵循C约定, 除了在C是未定义行为的转换。所有类型转换整型的行为在Rust都很好的定义。
fn main() {
let decimal = 65.4321_f32;
// Error! No implicit conversion
let integer: u8 = decimal;
// FIXME ^ Comment out this line
// Explicit conversion
let integer = decimal as u8;
let character = integer as char;
println!("Casting: {} -> {} -> {}", decimal, integer, character);
// when casting any value to an unsigned type, T,
// std::T::MAX + 1 is added or subtracted until the value
// fits into the new type
// 1000 already fits in a u16
println!("1000 as a u16 is: {}", 1000 as u16);
// 1000 - 256 - 256 - 256 = 232
println!("1000 as a u8 is : {}", 1000 as u8);
// -1 + 256 = 255
println!(" -1 as a u8 is : {}", (-1i8) as u8);
// For positive numbers, this is the same as the modulus
println!("1000 mod 256 is : {}", 1000 % 256);
// When casting to a signed type, the result is the same as
// first casting to the corresponding unsigned type then
// taking the two's complement.
// Unless it already fits, of course.
println!(" 128 as a i16 is: {}", 128 as i16);
// 128 as u8 -> 128, whose two's complement in eight bits is:
println!(" 128 as a i8 is : {}", 128 as i8);
// repeating the example above
// 1000 as u8 -> 232
println!("1000 as a i8 is : {}", 1000 as i8);
// and the two's complement of 232 is -24
println!(" 232 as a i8 is : {}", 232 as i8);
}
