#include <SI/length.h>

using namespace SI::literals; constexpr auto pitch = 2 / 1_mm; // OK, without constexpr, but need it

Expected behavior I expected to pitch to be of type 2 mm exp -1 (2 per millimeter) ratio of -1

I/include/SI/detail/unit.h:474:33: error: ‘(2 / 0)’ is not a constant expression

Hi ! Nice API that seems more user-friendly than boost. I'm testing it.

1/ Could be nice to add in your documentation ::value() how to cast a SI type to a type such a float. This is somewhat needed. I had to find it back from the code source.

auto a = 1.5_km;
std::cout << a.value() << std::endl;

Why not to add something like this ::to<T>() { return T(value()); } ? for example, a.to<int>() will return 1.

2/ Why degree_t is missing and how to write code such as 1.0_rad + 1.0_deg or degree_t d = 1.0_rad ? I tried this but does not compile:

using degree_t = SI::radian_t<double, std::ratio<10000, 572958>>;
degree_t a = 1.0_rad;
std::cout << a.value() << std::endl;

But only this odd code works:

using degree_t = SI::velocity_t<double, std::ratio<10000, 572958>>;
degree_t a = 1.0_m_p_s;
std::cout << a.value() << std::endl;

3/ You have types such as velocity and acceleration, we have to include the specific header files, but you have not jerk, jounce, crackle, pop (https://en.wikipedia.org/wiki/Fourth,_fifth,_and_sixth_derivatives_of_position), maybe is there a more generic way to generate them?

4/ Why I cannot display velocities ? The follow code

#include <SI/length.h>
#include <SI/time.h>
#include <SI/velocity.h>
#include <SI/stream.h>

auto a = 1.0_km / 1.0_s;
std::cout << a << std::endl;

will produce this error:

/usr/local/include/SI/stream.h: In instantiation of ‘std::ostream& operator<<(std::ostream&, const SI::detail::unit_t<_symbol, _exponent, _type, _ratio>&) [with char _symbol = 'v'; _exponent = std::ratio<1>; _type = long double; _ratio = std::ratio<1000, 1>; std::ostream = std::basic_ostream<char>]’:
main.cpp:17:17:   required from here
/usr/local/include/SI/stream.h:23:26: error: ‘str’ is not a member of ‘SI::unit_symbol<'v', std::ratio<1000, 1>, std::ratio<1> >’
   stream << unit.value() << SI::unit_symbol<_symbol, _ratio, _exponent>::str;

Have I missed an include (same for acceleration) ?

5/ This code works:

SI::metre_t<float> a = 1.5_km;
SI::seconds_t<float> s = 1.0_s;
SI::metre_per_second_t<float> c = a / s;

But this one fails to compile (because of the double to float conversion):

SI::metre_t<float> a = 1.5_km;
SI::metre_per_second_t<float> c = a / 1.0_s;

6/ I'm on the HEAD and not have conan but compilation will fail

 cmake ..
-- The CXX compiler identification is GNU 8.3.0
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Warning at test/CMakeLists.txt:24 (message):
  Conan not found.  Trying to find Catch2 without it.


-- Found Doxygen: /usr/local/bin/doxygen (found version "1.8.17 (d4a0825b1d00ead2ce441c3407d1983f80401353*)") found components: doxygen dot 
-- Configuring done
-- Generating done
-- Build files have been written to: /home/qq/SI/build

Then:

/home/qq/SI/test/src/benchmarks/unit_assignment_benchmarks.cc: In lambda function:
/home/qq/SI/test/src/benchmarks/unit_assignment_benchmarks.cc:18:37: error: ‘storage_for’ is not a member of ‘Catch::Benchmark’
       std::vector<Catch::Benchmark::storage_for<ratio_one_unit>> storage(

centi_metre_t a = 15; square_metre_t c = a / a; // This is not square meters!!! CHECK_ALMOST_EQUAL(c.value(), 1.0F, 1E-6);

The units of 'c' are not square metres! In fact 'c' does not have units. So why does this compile?

Dear Dominik

I am evaluating your great work. Before it may be used, it is always good idea to understand how it works. I wonder if you may add to documentation some details how the architecture works, how dimensions analyse works in your implementation, some very basic, may be few words. I suppose detail::unit_t is a most important class.

So far from documentation I know that it is: "type safety at compile time".

Hello,

First, thank you for this great library :)

Maybe I miss some point here but, is there an easy way to handle these two cases:

SI::metre_t<double> dx;
SI::metre_t<double> dy;
SI::seconds_t<double> dt;
SI::seconds_t<double> total_duration;
auto surface_flow = dx * dy / dt;  // compile error because there is no type for m^2/s
auto total_surface = dx * dy / dt * total_duration;  // compile error but there is a type for m^2

Regards and thank you.

• Hello ! First line:

A header only c++ library that provides type safety

Could be nice to explicitly say it is C++17 directly on the 1st line (else said on section "building & compat" which is far away).

• The illustrative example does not compile (g++ --std=c++17 foo.cpp). I git cloned the HEAD:

foo.cpp:9:46: error: ‘const struct SI::detail::unit_t<'M', std::ratio<1>, long double, std::ratio<1> >’ has no member named ‘as’
    9 | constexpr auto thousand_grams = one_kilogram.as<SI::gram_t>();
      |                                              ^~
foo.cpp:9:59: error: missing template arguments before ‘>’ token
    9 | constexpr auto thousand_grams = one_kilogram.as<SI::gram_t>();
      |                                                           ^
foo.cpp:9:61: error: expected primary-expression before ‘)’ token
    9 | constexpr auto thousand_grams = one_kilogram.as<SI::gram_t>();
      |  

Trying to calculate acceleration from force divided by mass (Newton's second law), but it gives me a compile error.

When I try to add: BUILD_UNIT_FROM_DIVISON(acceleration_t, force_t, mass_t) ...in acceleration.h, I get even more compiler errors, looks like an issue where header include orders.

Reproduced in "SI" version 1.4.1, using clang 7.0.1-8, gcc 8.3.0 and VS2019 16.4.3

If you have an Length object and you call obj.value() it may not be clear what unit it returns eg. // somewhere in the code SI::milli_metre_t<long double> x{100}; //somewhere else in the code x.value(); // is this in millimeter or meter?

Provide a way to clearly describe what magnitude the raw value should represent eg. constexpr long double value_as(const Length u) { return (*this/u).value()} //usage long double m = x.value_as(meter); // m=0.1 long double mm = x.value_as(millimeter); // mm=100

Describe alternatives you've considered Use value() and track base unit in comments or notes

Is your feature request related to a problem? Please describe.

Dear

I would like test your library, however I have problem with run unit tests "out of the box". I think the instructions: mkdir build cd build cmake .. cmake --build . --config Debug -- -j $(nproc)

does not cover unit tests because unit test are not build.

1. Did I missed understand something? (I use cmake 3.17 VS2017, gcc 9.2, windows host)
2. I also do not understand installing instruction since it is header library.

/Greg

Defining constants of derived data types could be more intiutive, as we have to always give a number before a literal: auto SPEED_CONSTANT = 10_km / 1_h;

How about allowing the line below or similar: auto SPEED_CONSTANT = 10_km/h;

Obviously, the users of SI library, needs to input values at runtime and view outputs from applications

In my opinion, if I use a certain physical unit in a determinate scale, I want to see (for default) the variable's value in the scale I chose, with the related symbol

I am a C ++ amateur and certainly I cannot afford to offer you solutions, especially about generic programming, with extensive use of templates

Is your feature request related to a problem? Please describe.

Hi sir ! Make a long time since https://github.com/bernedom/SI/issues/93 I still have not yet converted my float into SI in my personal project :( I'm currently testing your library back and at the same time testing this one https://github.com/nholthaus/units.

To help beginners starting with your lib, I think you could add some concrete some basic examples in your documentation. Here is an attempt of mine concerning tricycle kinematics. https://github.com/Lecrapouille/BacASable/tree/master/LawControl/SI

The code using your lib is here https://github.com/Lecrapouille/BacASable/blob/master/LawControl/SI/si.cpp and the code using units is here https://github.com/Lecrapouille/BacASable/blob/master/LawControl/SI/units.cpp (feel free to use this code).

I'm sorry, time is currently missing for me for writing this ticket (I do it anyway else I'll forget to write it), as well for making a C++ class of si.cpp like done in units.cpp, but currently si.cpp does note compile because (speed / wheelbase) fails compiling (I hope the issue does not come from me). In addition, I noticed some weak points compared to the other lib:

Operators that could be overloaded:

• The x += dt * ... does not compile, we have to write x = x + dt * ... instead.
• The << speed does not compile. We have to write << speed.value() instead (same for x, heading). In the other lib the unit is also displayed (like 2 mps).
• Less important but si::cos(heading) does not exist, we have to write instead std::cos(heading.value()) this just make the code more compact but let possible mistake like std::cos(x.value()) with x typed of metre_t.

Describe the solution you'd like

• Implement overloading operators such as +=, <<, cos() ...
• Add some basic examples using your lib.
• In your documentation, you are using auto but it is better to give the real type like SI::metre_t<double> because we have to find their type back when passing them as function arguments.

Describe alternatives you've considered Implemented in https://github.com/nholthaus/units.

Additional context n/a