Package unsafe is used extensively within low-level packages like runtime, os, syscall, and net that interact with the operating system, but is almost never needed by ordinary programs.
* The unsafe.Sizeof function reports the size in bytes of the representation of its operand, which may be an expression of any type; the expression is not evaluated. A call to Sizeof is a constant expression of type uintptr , so the result may be used as the dimension of an array type, or to compute other constants.
* The unsafe.Alignof function reports the required alignment of its argument’s type. Like Sizeof, it may be applied to an expression of any type, and it yields a constant.
* The unsafe.Offsetof function, whose operand must be a field selector x.f, computes the offset of field f relative to the start of its enclosing struct x, accounting for holes, if any.
* Most pointer types are written *T , meaning ‘‘a pointer to a variable of type T . ’’ The unsafe.Pointer type is a special kind of pointer that can hold the address of any variable.
```
import "unsafe"
fmt.Println(unsafe.Sizeof(float64(0))) // "8"
```