boostorg/hana

Your standard library for metaprogramming

Jason Rice

@ricejasonf

ah right

Maik Klein

@MaikKlein

    static_assert(size != 0 || size >= 1, "Empty");
    static_assert(size == 1 || size == 0, "More than 1");

Should be what I want, but that seems way too complicated for something so simple

Jason Rice

@ricejasonf

here is a much, much simpler solution and the good news is it only generates one warning :P

#include<type_traits>

template<int size, typename = void>
struct SizeChecker
{ };

template<int size>
struct SizeChecker<size,
  std::enable_if_t<(size == 0)>>
{
  static_assert(size == 0, "Does not contain anything");
};

template<int size>
struct SizeChecker<size,
  std::enable_if_t<(size > 1)>>
{
  static_assert(size > 1, "Contains duplicates");
};

int main()
{
  constexpr int size = 1;
  SizeChecker<size>{};
}

Maik Klein

@MaikKlein

haha

Jason Rice

@ricejasonf

sorry that's all i got

Maik Klein

@MaikKlein

It appears that I was very confused and you can actually write it like this static_assert( size != 0, "Must not be empty") and static_assert(size <= 1, "Too many")

I think the trigger at false must have confused me somehow

Jason Rice

@ricejasonf

ah right It would check the second one after asserting that it wasn't 0

Maik Klein

@MaikKlein

Jason Rice

@ricejasonf

meaning you can't get two failures

Maik Klein

@MaikKlein

I can only get one failure

Jason Rice

@ricejasonf

yeah.. nm :)

Maik Klein

@MaikKlein

because for 0, 0 <= 1 is true

Jason Rice

@ricejasonf

@MaikKlein Regarding your question about 'previous template instantiations', precompiled header files might be the answer. I'm not sure to what extent it would make a difference, but it shaves off about 5 seconds (from 8 seconds total) from my convoluted primality test. A more extreme case could be tested by fiddling with the upper end of the range in expensive.hpp.

https://gist.github.com/ricejasonf/a0807dc082950cffcd2b

As you can see in the Makefile you can compile a .pch just like you can an object file.

Jason Rice

@ricejasonf

Apparently clang has modules implemented. I wonder if it would be feasible to export that map variable and tell clang to fully evaluate/optimize the AST to output a pch or header file that leaves all of the cruft behind.

Maik Klein

@MaikKlein

@ricejasonf interesting, haven't used pch's yet.

btw is there a way to benchmark the compile time? I tried -ftime-report in clang but it's not very helpful.

Maik Klein

@MaikKlein

I am thinking of something like

foo<a,b,c,d> at line 24 in foo.hpp took 1.54 seconds to instantiate.

Maybe this? https://github.com/mikael-s-persson/templight

Jason Rice

@ricejasonf

@MaikKlein idk. I was just using time make and it appears that Hana uses a ruby script that calls a make command

Maik Klein

@MaikKlein

I guess that works okay for isolated code, but I would really like to see where the bottleneck is in my current code base. I'll have a look at clang modules now and see if they give me any benefit.

Maik Klein

@MaikKlein

I guess I am also going to try templight, it even integrates kcachegrind

https://github.com/mikael-s-persson/templight-tools/blob/master/images/kcachegrind_snap1.png

^ wtf is that image

ah it's his profile picture

Jason Rice

@ricejasonf

this oss?

your project that is

Maik Klein

@MaikKlein

My project will be open source

not sure if that is what you asked though :d. I am not the creator of templight

Jason Rice

@ricejasonf

is it on github?

Maik Klein

@MaikKlein

Not yet, it's in a very early state. It will be a 2d game framework with an entity component system.

Louis Dionne

@ldionne

@MaikKlein To find the compile-time bottlenecks in your code, first isolate the TUs that are problematic. Then, what I usually do is simply comment out instantiations and compile over and over with time clang++ ….

Also, I just found out about ccache. It caches files between compilations, and it’s really awesome (from what I can see so far).

Jason Rice

@ricejasonf

@ldionne I'm not sure if manual intervention is required for Travis to include my third commit and cancel the builds for the second commit.

I keep getting "There was an error while loading data, please try again" on the linked status page.

Louis Dionne

@ldionne

@ricejasonf It will automatically test any new commit that you push, and you can just leave it do its job on the current commits, even though that’s not strictly required.

Which status page?

Jason Rice

@ricejasonf

https://travis-ci.org/boostorg/hana/builds/96113600

Louis Dionne

@ldionne

I can see the jobs just fine.

Jason Rice

@ricejasonf

same link and everything... weird but nbd

Jason Rice

@ricejasonf

@ldionne It says some checks were not successful. I still see the error page on travis. :scream:

Louis Dionne

@ldionne

@ricejasonf It’s fine, it was just a timeout when downloading Boost. I restarted that job.

@ricejasonf Would you mind squashing these commits together, and then push —forceing to update the PR?

Otherwise, I can just squash it myself; you decide.

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