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added a bit of documentation

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Yves Delley
2024-05-12 11:13:00 +02:00
parent c0efdb1790
commit f30fac17f0
4 changed files with 26 additions and 10 deletions
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docs/users_guide/framework_basics/value_conversions.md
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@@ -147,3 +147,17 @@ using namespace unit_symbols;
Price price{12.95 * USD};
Scaled spx = value_cast<USD_s, std::int64_t>(price);
```
As a shortcut, instead of providing a unit and a representation type to `value_cast`, you may also provide a
`Quantity` type directly, from which unit and representation type are taken. However, `value_cast<Quantity>`,
still only allows for changes in unit and representation type, but not changing the type of the quantity.
For that, you will have to use a `quantity_cast` instead.
Overloads are also provided for instances of `quantity_point`. Furthermore, in that case, there is
an overload `value_cast<ToQP>(qp)`, which is roughly equivalent to
`value_cast<typename ToQP::quantity_type>(qp).point_for(ToQP::point_origin)`.
In contrast to a separate `value_cast` followed by `point_for` (or vice-versa), the combined
`value_cast` tries to choose the order of the individual conversion steps in such a way,
to avoid both overflow and unnecessary loss of precision. Overflow is a risk because the change of origin point
may require an addition of a potentially large offset (the difference between the origin points),
which may well be outside the range of one or both quantity types.