Documentation - QuantityMaker(QuantityD) troubleshooting

[connorjak]

When work in progress while converting code to use units, I notice a lot of my errors narrow down to this:

QuantityD<Radians> recently_returning_quantityd_function()
{
  ...
}

auto mu = recently_returning_quantityd_function();
auto mu_2 = radians(mu); //quantitymaker on a quantity

This case isn't covered by the troubleshooting documentation here: https://aurora-opensource.github.io/au/main/troubleshooting. The errors in MSVC are also a bit difficult to use to discover the issue. I'm not sure if there's a code change to make for better asserts for this, but maybe this case should be added to the troubleshooting documentation.

[connorjak]

Here is a portion of the relevant MSVC 14.40 error log:

C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.40.33807\include\type_traits(1338): error C2794: 'type': is not a member of any direct or indirect base class of 'std::common_type<au::Quantity<au::Radians,double>,double>'
  C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.40.33807\include\type_traits(1338): note: the template instantiation context (the oldest one first) is
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\server\CoreMath\Orbital.h(215): note: see reference to function template instantiation 'au::Quantity<au::Radians,double>::Quantity<au::Radians,au::Quantity<au::Radians,double>,void>(au::Quantity<au::Radians,au::Quantity<au::Radians,double>>)' being compiled
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\server\CoreMath\Orbital.h(215): note: see the first reference to 'au::Quantity<au::Radians,double>::Quantity' in 'st_orbit::getElemsfromState'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: see reference to function template instantiation 'auto au::Quantity<au::Radians,au::Quantity<au::Radians,double>>::as<double,au::Radians,void>(NewUnit) const' being compiled
          with
          [
              NewUnit=au::Radians
          ]
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3761): note: see reference to alias template instantiation 'std::common_type_t<au::Quantity<au::Radians,double>,double>' being compiled
C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au\au_all_units.h(3761): error C2938: 'std::common_type_t' : Failed to specialize alias template
C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au\au_all_units.h(3765): error C2672: 'au::detail::apply_magnitude': no matching overloaded function found
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3631): note: could be 'T au::detail::apply_magnitude(const T &,au::Magnitude<BP2s...>)'
C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au\au_all_units.h(3764): error C2672: 'au::make_quantity': no matching overloaded function found
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3652): note: could be 'auto au::make_quantity(T)'
C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au\au_all_units.h(3736): error C2665: 'au::Quantity<au::Radians,double>::Quantity': no overloaded function could convert all the argument types
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(4013): note: could be 'au::Quantity<au::Radians,double>::Quantity(double)'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: 'au::Quantity<au::Radians,double>::Quantity(double)': cannot convert argument 1 from 'void' to 'double'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: Expressions of type void cannot be converted to other types
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3747): note: or       'au::Quantity<au::Radians,double>::Quantity(au::Zero)'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: 'au::Quantity<au::Radians,double>::Quantity(au::Zero)': cannot convert argument 1 from 'void' to 'au::Zero'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: Expressions of type void cannot be converted to other types
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3755): note: or       'au::Quantity<au::Radians,double>::Quantity(T &&)'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: 'au::Quantity<au::Radians,double>::Quantity(T &&)': could not deduce template argument for '__formal'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3754): note: 'au::CorrespondingQuantityT' : Failed to specialize alias template
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3686): note: 'Unit': is not a member of any direct or indirect base class of 'au::CorrespondingQuantity<T>'
          with
          [
              T=void
          ]
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3744): note: or       'au::Quantity<au::Radians,double>::Quantity(au::Quantity<OtherUnit,OtherRep>)'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: 'au::Quantity<au::Radians,double>::Quantity(au::Quantity<OtherUnit,OtherRep>)': could not deduce template argument for 'au::Quantity<OtherUnit,OtherRep>' from 'void'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3735): note: or       'au::Quantity<au::Radians,double>::Quantity(au::Quantity<OtherUnit,OtherRep>)'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: 'au::Quantity<au::Radians,double>::Quantity(au::Quantity<OtherUnit,OtherRep>)': could not deduce template argument for 'au::Quantity<OtherUnit,OtherRep>' from 'void'
  C:\Users\conno\Documents\SC\UE5\SC_Platform\Compute_Server\externals\Au/au_all_units.h(3736): note: while trying to match the argument list '(void)'

[chiphogg]

Thanks for calling this out! As you say, there are really two issues here: better error messages for trying to "quantitify" a quantity, and giving our troubleshooting guide a refresh. I think we should do both.

At the moment, I can't pick up new work items until I have my CppCon 2024 slides up to "dry run" standards. The dry run will probably be Sep. 2 or 3. In the meantime, I'll write down the things I think we should do to close this item out.

• Add static_assert in Quantity and QuantityPoint for IsValidRep
• Add operator() specialization in QuantityMaker and QuantityPointMaker for Quantity and QuantityPoint, to give very direct error message
• Add new section to the troubleshooting guide for this kind of error (perhaps doing Provide more flexible alternative to integer_quotient() #253 at the same time)

The troubleshooting guide is definitely due for a refresh. I'll probably do that aspect of it at the same time as #253 (which I've solved in my local client, and just need to get out for review).

So, I'd say this has a pretty good chance of being addressed sometime in September.

[chiphogg]

@connorjak, check out this comment to see the before-and-after on the error messages for the implementation that's currently under review. (Fair warning: you'll have to scroll through a lot of "before" to even get to the "after"!)