Zero

Zero is a type that represents a quantity of “0” in any units. See the Zero discussion doc for more background motivation and use cases.

Zero is a monovalue type. Every instance of Zero is equivalent to every other instance. In practice, it’s easiest and most idiomatic to use the predefined instance, ZERO.

Conversions

The goal is for ZERO to be implicitly convertible to any type for which the value of “0” is completely unambiguous. For types in the language or the standard library, which cannot possibly know about Zero, we do this via implicit conversions. For other types, we do this by adding a constructor which takes Zero.

Implicit conversions

We provide implicit conversions to the following categories of types:

• Any arithmetic type (int, double, std::size_t, …).

• Any std::chrono::duration type.

Quantity constructor

Quantity is implicitly constructible from Zero.

This means you can efficiently check the sign of any Quantity by comparing to ZERO.

QuantityPoint constructor

This is explicitly deleted. There is no unambiguous notion of which point is labeled as “0”; it depends on the choice of units. Therefore, we delete this constructor to prevent users from relying on this dubious notion.

I/O

If you include I/O support, then Zero will be streamed as "0".