Re: [PATCH v5 1/7] rust: time: make Delta generic over its time unit

[FUJITA Tomonori <tomo@flapping.org>]

On Thu, 06 Aug 2026 11:44:21 +0200
Andreas Hindborg <a.hindborg@kernel.org> wrote:

>> +/// A time unit of nanoseconds.
>> +///
>> +/// A [`Delta<Nsec>`] stores its value as `i64` nanoseconds and can represent
>> +/// any `i64` value, including negative, zero, and positive numbers.
>> +#[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord, Debug)]
>> +pub struct Nsec;
> 
> Should we make these enum with zero variants to indicate they should not
> be constructed?

Good idea, I will change it in v6.

>> +
>> +impl TimeUnit for Nsec {
>> +    type Repr = i64;
>> +}
>> +
>>  /// A span of time.
>>  ///
>> -/// This struct represents a span of time, with its value stored as nanoseconds.
>> -/// The value can represent any valid i64 value, including negative, zero, and
>> -/// positive numbers.
>> +/// The span is stored in the unit given by the type parameter `U` (see
>> +/// [`TimeUnit`]); its value has type `U::Repr`. `U` defaults to [`Nsec`], so a
>> +/// plain [`Delta`] is a span in nanoseconds. The value can be negative, zero, or
>> +/// positive.
>>  #[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord, Debug)]
>> -pub struct Delta {
>> -    nanos: i64,
>> +pub struct Delta<U: TimeUnit = Nsec> {
>> +    value: U::Repr,
>>  }
>>  
>>  impl ops::Add for Delta {
> 
> When you add `Jiffy` later, this impl block will only cover
> `Delta<Nsec>`. Is that intentional, or did you intend to support
> all these operations operations for `Delta<Jiffy>` as well?

Intentional. Delta<Jiffy> exists to carry a jiffies-valued timeout
across the C boundary; it is not meant as a general arithmetic type. I
can add them if a user needs them.