C++ Weekly - Ep 420 - Moving From C++17 to C++20 (More constexpr!)

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[@emccartney]

I still think it would be really interesting to compare the binary size & runtime performance of your project over the succesive upgrades!

[@cppweekly]

Noted: github.com/lefticus/cpp_weekly/issues/373

[@KvotheP]

Are you sure that default spaceship operator is doing the right thing?

[@munkeys]

I had the same thought.

[@obinator9065]

no, it's drinking water.

[@AlexanderPetersonml]

I can never remember if it's doing the left thing

[@cppweekly]

It's job is to do a member wise comparison in order of declaration. If it's not doing the right thing this would be a bug in the compiler, no?
Did I miss something?

[@sandordargo8838]

@@cppweekly If it does member wise comparison than RN(6, 4) > RN(3, 2) but I'm almost sure we can find more similar issues.

[@jessmutant]

I think you want to revisit the comparison operator. By using the default implementation, you are getting an order that is not mathematically correct (e.g. with this, 1/2 is less than 1/3 !).
On another note, I enjoyed this series very much, watching code morph from broken javaesque-C++ to full constexp modern C++.

[@cppweekly]

Ah, ok, I see the point.

[@MarekKnapek]

Constexpr all the things. Not really. Recently, I implemented the Triple DES encryption algorithm in C++14 constexpr (I already had AES). I took the ~2000 test cases from NESSIE project and static asserted my correctness. Compilation time is ~45 minutes and ~10 GB RAM. If I run the tests in run-time instead, it takes merely seconds to compile and run.

[@AlexanderPetersonml]

What if you use the "optimize for size" flag?

[@LordPlebulus]

Are you going to do any performance benchmarks after the c++23 upgrade? I'd be curious to see the impact of constexpr & modern c++ features.

[@cppweekly]

I'll make a note to do that.

[@anon_y_mousse]

Maybe I'm weird, but I'm actually really excited about UDL's. I've been working on adding that feature to my own language complete with a unit of measurement conversion module. I've been thinking of all kinds of uses for it that probably weren't intended for C++, but most certainly will be for my own language. For instance, being able to coerce a formula involving constants into a particular type. You would have to use quotes in C++, which is fine, but not as nice to use.

[@LaserFur]

I have a problem with C++ 20 in VS2019 where I am deriving a template aggregate class from a base type as a simple form of a "strong type". For some reason I had to change back to C++17 to get it to compile. I'll try again after updating to a newer version of VS.

[@FedericoPekin]

awesome

[@MrModez]

Now show the binary size :)

[@cppweekly]

Noted to compare: github.com/lefticus/cpp_weekly/issues/373

[@yunuszenichowski]

hihi 420 :>)