Casting

In Odin, there are numerous types of casts:

• cast Basic cast
• transmute Convert the bits of one type to another of the same size
• union_cast Convert from a union type to its variant

main :: proc() {
// `cast`
    x: i32 = 123;
    y: i64 = cast(i64)x;

    // Named types are distinct from their base type
    Seconds :: i64;
    elapsed_time := 2 * Seconds;
    raw_number: i64 = cast(i64)elapsed_time;
    // TODO: Try removing the above cast and see what happens

// `transmute`
    // See: https://en.wikipedia.org/wiki/Fast_inverse_square_root
    Q_rsqrt :: proc(number: f32) -> f32 {
        threehalfs :: 1.5;

        x2: f32 = number * 0.5;
        y: f32 = number;
        i: i32 = transmute(i32)y;                       // evil floating point bit level hacking
        i = 0x5f3759df - ( i >> 1 );                // what the fuck? 
        y = transmute(f32)i;
        y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration
    //  y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed
        return y;
    }

// `union_cast`
    Entity :: union {
        // Common fields
        id:          u64,
        position:    [vector 3]f32,
        orientation: quaternion128,
        name:        string,

        // Variants
        Frog{
            jump_height:   f32,
            ribbit_volume: f32,
        },
        Door{
            openness: f32,
        },
        Monster{
            speed:        f32,
            scary_factor: int,  
        },
    }

    e: Entity = Entity.Frog{id = 123, name = "Frank", jump_height = 2.2};

    // Value and `ok` if valid
    f1, ok := union_cast(Entity.Frog)e;
    // Ignore the check
    f2, _ := union_cast(Entity.Frog)e;

    // Panics if the cast is not possible
    f3 := union_cast(Entity.Frog)e;
}