Merge branch 'master' into add_fma

.github/workflows/documentation.yml

@@ -34,6 +34,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - uses: actions/setup-python@v4
         with:
           python-version: 3.x
@@ -46,7 +48,7 @@ jobs:
             mkdocs-material-
       - name: Installing pip packages
         run: |
-          pip install conan mkdocs-material mike
+          pip install conan mkdocs-material mkdocs-rss-plugin mike
       - name: Prepare git
         run: |
           git config --global user.name github-actions

docs/blog/.authors.yml

@@ -0,0 +1,6 @@
+authors:
+  mpusz:
+    name: Mateusz Pusz
+    description: Creator
+    avatar: https://avatars.githubusercontent.com/u/506260
+    url: https://github.com/mpusz

docs/blog/index.md

@@ -0,0 +1 @@
+# Blog

docs/blog/posts/2.0.0-released.md

@@ -0,0 +1,130 @@
+---
+date: 2023-09-24
+authors:
+  - mpusz
+categories:
+  - Releases
+---
+
+# What's new in mp-units 2.0?
+
+**After a year of hard work, we've just released mp-units 2.0.0. It can be obtained from
+[GitHub](https://github.com/mpusz/mp-units/releases/tag/v2.0.0) and
+[Conan](https://conan.io/center/recipes/mp-units?version=2.0.0).**
+
+In this post, we will describe all the changes introduced by the new version.
+
+<!-- more -->
+
+## Why 2.0 if 1.0 was never released?
+
+Version 2 of the **mp-units** project is a huge change and a new quality for the users.
+We did not want to pretend that 2.0 is an evolutionary upgrade of the previous version of the
+project. It feels like a different product.
+
+We could start a new repo named "mp-units-v2" similarly to [range-v3](https://github.com/ericniebler/range-v3)
+but we decided not to go this path. We kept the same repo and made the scope of the changes and
+potential breakage explicit with a drastic bump in the project version.
+
+## What has changed?
+
+The answer is "nearly everything". The whole library and its documentation were rewritten nearly
+from scratch.
+
+Here are the significant changes that the users can observe:
+
+- **Repository name**
+
+    If you didn't notice, the repository name was changed from "mpusz/units" to "mpusz/mp-units".
+
+- **Header files content and layout**
+
+    Previously, all the header files resided in the _include/units_ directory, and now they can be
+    found in _include/mp-units_. The project file tree was significantly changed as well. Many
+    files were moved to different subdirectories or renamed.
+
+- **Namespace**
+
+    Previously, all the definitions were provided in the `units` namespace, and now they are in the
+    `mp_units` one.
+
+- **Abstractions, interfaces, definitions**
+
+    The interfaces of all of the types were refactored, and we have a new way to construct a `quantity`
+    and `quantity_point`, we got unit symbols, and nearly all of the template arguments are now passed
+    by values thanks to class NTTP extensions in C++20. Also, systems definitions are much terser now
+    thanks to a new design approach.
+
+*[NTTP]: Non-Type Template Parameter
+
+- **Conan 2.0**
+
+    Also, now we support Conan 2.0, which provides an updated way of handling dependencies.
+
+## What is gone?
+
+Some cornerstones of the initial design did not prove in practice and were removed while
+we moved to version 2.
+
+### The downcasting facility
+
+The first and the most important of such features was removing the downcasting facility.
+This feature is still a powerful metaprogramming technique that allows users to map long class template
+instantiations to nicely named, short, and easy-to-understand user's strong types.
+
+Such mapping works perfectly fine for 1-to-1 relationships. However, we often deal with N-to-1 connections in the quantities and units domain. Here are only a few such examples:
+
+- _work_ and _torque_ have the same dimension $L^2MT^{-2}$,
+- becquerel and hertz have the same definition of $s^{-1}$,
+- litre and cubic decimetre have the same factor.
+
+In the above examples, multiple entities "wanted" to register different names for identical class
+template instantiations, resulting in compile-time errors. We had to invent some hacks and
+workarounds to make it work, but we were never satisfied with the outcome.
+
+Additionally, this facility could easily lead to ODR violations or provide different results
+depending on which header files were included in the translation units. This was too vulnerable
+to be considered a good practice here.
+
+*[ODR]: One Definition Rule
+
+### No UDLs anymore
+
+Over the years, we have learned that UDLs are not a good solution either. More information on this
+subject can be found in the
+[Why don't we use UDLs to create quantities?](../../getting_started/faq.md#why-dont-we-use-udls-to-create-quantities)
+chapter.
+
+*[UDL]: User-Defined Literals
+
+
+## New look and feel
+
+Here is a concise example showing you the new look and feel of the library:
+
+```cpp
+#include <mp-units/format.h>
+#include <mp-units/systems/isq/isq.h>
+#include <mp-units/systems/si/si.h>
+#include <format>
+
+using namespace mp_units;
+using namespace mp_units::si::unit_symbols;
+
+quantity<isq::speed[m / s]> avg_speed(quantity<si::metre> d,
+                                      quantity<si::second> t)
+{ return d / t; }
+
+int main()
+{
+  auto speed = avg_speed(220 * km, 2 * h);
+  std::println("{}", speed);  // 30.5556 m/s
+}
+```
+
+All of the changes we provided, although breaking ones, resulted in much better,
+easier, and safer abstractions. These offer a new quantity on the market and hopefully will be
+appreciated by our users.
+
+Please check our new documentation to learn about the latest version of the project and find out
+how to benefit from all the new cool stuff we have here.

docs/blog/posts/kona-2023-report.md

@@ -0,0 +1,50 @@
+---
+date: 2023-11-12
+authors:
+  - mpusz
+categories:
+  - WG21
+---
+
+# Report from the Kona 2023 ISO C++ Committee meeting
+
+**Several groups in the ISO C++ Committee reviewed the [P1935: A C++ Approach to Physical Units](https://wg21.link/p1935)
+proposal in Belfast 2019 and Prague 2020. All those groups expressed interest in the potential
+standardization of such a library and encouraged further work. The authors also got valuable
+initial feedback that highly influenced the design of the V2 version of the mp-units library.**
+
+In the following years, we scoped on getting more feedback from the production and design and
+developed version 2 of the **mp-units** library that resolves many issues raised by the users and
+Committee members. The features and interfaces of this version are close to being the best we can
+get with the current version of the C++ language standard.
+
+<!-- more -->
+
+For the last ISO C++ Committee meeting, we provided three new proposals related to the
+standardization of the quantities and units library:
+
+- [P2980: A motivation, scope, and plan for a physical quantities and units library](https://wg21.link/p2980R1),
+- [P2981: Improving our safety with a physical quantities and units library](https://wg21.link/p2981R1),
+- [P2982: `std::quantity` as a numeric type](https://wg21.link/p2982R1).
+
+Those were reviewed and briefly discussed in several groups: Numerics (SG6), Safety & Security
+(SG23), and Library Evolution Working Group (LEWG). Most of the feedback was positive, and
+the Committee is interested in spending more time on such proposals.
+
+!!! question "LEWG POLL: Given that our time is limited, more time should be promised for a quantities and units library"
+
+    | SF | F  | N | A | SA |
+    |----|----|---|---|----|
+    | 10 | 13 | 4 | 0 | 0  |
+
+    Attendance: 22 + 6
+
+    Number of Authors: 4
+
+    Authors’ position: 4x SF
+
+    Outcome: Strong consensus in favor
+
+Additionally, some concerns were raised about the large scope of the proposal. We were encouraged
+to come back with more details and design rationale in a unified paper. This is what we are working
+on now for the next Committee meeting that will happen in mid-March 2024 in Tokyo.

mkdocs.yml

@@ -51,6 +51,14 @@ theme:
 
 # Plugins
 plugins:
+  - blog
+  - rss:
+      match_path: blog/posts/.*
+      date_from_meta:
+        as_creation: date
+      categories:
+        - categories
+        - tags
   - search
   - tags:
       tags_file: users_guide/examples/tags_index.md
@@ -108,6 +116,8 @@ nav:
       - Quick Start: getting_started/quick_start.md
       - Installation and Usage: getting_started/installation_and_usage.md
       - FAQ: getting_started/faq.md
+  - Blog:
+      - blog/index.md
   - User's Guide:
       - Terms and Definitions: users_guide/terms_and_definitions.md
       - Framework Basics:

requirements.txt

@@ -2,4 +2,5 @@ conan
 pre-commit
 identify
 mkdocs-material
+mkdocs-rss-plugin
 mike

src/utility/include/mp-units/math.h

@@ -144,18 +144,12 @@ template<auto R, typename Rep>
  * @param b: Addend
  * @return Quantity: The nearest floating point representable to ax+b
  */
-
 template<auto R, auto S, auto T, typename Rep1, typename Rep2, typename Rep3>
 [[nodiscard]] constexpr QuantityOf<common_quantity_spec(get_quantity_spec(R) * get_quantity_spec(S),
                                                         get_quantity_spec(T))> auto
-fma(  // QuantityOf takes a QuantitySpec as an argument
-  const quantity<R, Rep1>& a, const quantity<S, Rep2>& x, const quantity<T, Rep3>& b) noexcept
-  requires requires {
-    common_quantity_spec(get_quantity_spec(R) * get_quantity_spec(S), get_quantity_spec(T));
-  } &&  // or just common_reference but I wanted to express that the quantity types must match here and we don't care
-        // too much about units
-           (get_unit(R) * get_unit(S) ==
-            get_unit(T)) &&  // units that we want to add are equivalent (have the same magnitude)
+fma(const quantity<R, Rep1>& a, const quantity<S, Rep2>& x, const quantity<T, Rep3>& b) noexcept
+  requires requires { common_quantity_spec(get_quantity_spec(R) * get_quantity_spec(S), get_quantity_spec(T)); } &&
+           (get_unit(R) * get_unit(S) == get_unit(T)) &&
            (
              requires {
                fma(a.numerical_value_ref_in(a.unit), x.numerical_value_ref_in(x.unit),
@@ -168,7 +162,8 @@ fma(  // QuantityOf takes a QuantitySpec as an argument
 {
   using std::fma;
   return quantity{
-    fma(a.numerical_value_ref_in(a.unit), x.numerical_value_ref_in(x.unit), b.numerical_value_ref_in(b.unit)), T};
+    fma(a.numerical_value_ref_in(a.unit), x.numerical_value_ref_in(x.unit), b.numerical_value_ref_in(b.unit)),
+    common_reference(R * S, T)};
 }
 
 

test/unit_test/runtime/math_test.cpp

@@ -67,6 +67,11 @@ TEST_CASE("'fma()' on quantity changes the value and the dimension accordingly",
   REQUIRE(fma(1.0 * isq::length[m], 2.0 * one, 2.0 * isq::length[m]) == 4.0 * isq::length[m]);
 }
 
+TEST_CASE("'fma()' returns a common reference.", "[math][fma]")
+{
+  REQUIRE(fma(isq::speed(10.0 * m / s), isq::time(2.0 * s), isq::height(42.0 * m)) == isq::length(62.0 * m));
+}
+
 
 TEST_CASE("'pow<Num, Den>()' on quantity changes the value and the dimension accordingly", "[math][pow]")
 {