There are safe interfaces for this stuff too. The byteorder crate (not in the standard library, but widely used) has: let i = NativeEndian::read_i64(...);

There are safe interfaces for this stuff too. The byteorder crate (not in the standard library, but widely used) has: let i = NativeEndian::read_i64(...); Or if you're literally parsing a string of digits: let i: Option<i64> = digits.parse(); The `parse` method on strings is a particularly smooth piece of trait system magic.