Building with C++17 standard and Boost results in use of removed functions

[dgovil]

This is more of an informational issue rather than anything dire, but I figure it's good to log it, since I know I'm not the only one trying to build USD as C++17. However, Boost is an issue because Boost has a bunch of functions that are removed from C++17 as the default pathway.

A lot of USD files use the Boost hash.hpp file that makes use of the deprecated std::unary_function call by default.
Depending on your compiler version, this will print a warning (if its deprecated but not removed), but starting with the most recent clang versions (as of macOS 14 / Xcode 15 for example), it is actually removed, resulting in this error:

boost/container_hash/hash.hpp:132:33: error: no template named 'unary_function' in namespace 'std'; did you mean '__unary_function'?
        struct hash_base : std::unary_function<T, std::size_t> {};
                           ~~~~~^

There's a couple workarounds for this, until USD is successfully de-boosted.

1. Obviously , the easiest workaround is don't compile for C++17 and stick with C++14. But that's dull 😀
2. Compile with Boost 1.82 per the 2024 VFX Platform, but that might not be possible for you either because of other dependencies
3. Add add_compile_definitions(BOOST_NO_CXX98_FUNCTION_BASE) to your CMake file somewhere, or just make sure it's defined before Boost is included. That is used across various Boost functions and makes Boost be C++17 compatible.

Anyway, again, not so much something that explicitly needs solving. I'm just putting this up as an FYI for anyone else hitting it.
I assume that when USD moves to C++17, that the define will need to be set, or we'll be free of boost before then.

[sunyab]

That's great information! We're looking to move to C++17 so we can replace some boost classes (like boost::optional) with their std equivalents as part of the de-boostification effort. It looks like we'll need to set that BOOST_NO_CXX98_FUNCTION_BASE in our CMake in the interim.

Thanks for the heads-up!

[meshula]

We probably need to also publish BOOST_NO_CXX98_FUNCTION_BASE to our pxrConfig.cmake files in addition to setting it in build_usd.py, because anything consuming USD is also affected. For my own usage, I have been building against boost 1.81 (1.81 was the oldest boost that worked in my regression) in order to avoid having to introduce BOOST_NO_CXX98_FUNCTION_BASE to downstream projects.

[jesschimein]

Filed as internal issue #USD-8638

[nvmkuruc]

It should be relatively straight forward to replace boost::hash with TfHash in imaging to avoid needing to worry about BOOST_NO_CXX98_FUNCTION_BASE.

[dgovil]

@meshula and @nvmkuruc , is this issue still problematic for USD 23.11? I see that the Boost versions in the build_usd.py are still pretty old so I think we'd still hit this, but maybe all the uses of boost:hash have been removed?

If not, I think we might need to upgrade the Boost version used?

[sunyab]

Hey @dgovil, we have not removed all uses of boost::hash but the C++17 issue should be addressed by a couple of changes:

• 0e4d360 adds the preprocessor define that @meshula mentioned above to the USD build, so USD itself shouldn't hit this issue.
• ae45ce8 removes the last uses of boost::hash from public headers, so client code that happens to include them shouldn't hit this issue either.

[dgovil]

Awesome. Thanks, @sunyab. I'll close this issue out since it's not blocking anymore.

[ikryukov]

@dgovil @sunyab I'm still have this issue with 23.11 compiled with python support:

[build] In file included from /Users/ikryukov/work/USD_build_23_11/include/pxr/imaging/hd/task.h:29:
[build] In file included from /Users/ikryukov/work/USD_build_23_11/include/pxr/imaging/hd/driver.h:31:
[build] In file included from /Users/ikryukov/work/USD_build_23_11/include/pxr/base/vt/value.h:31:
[build] In file included from /Users/ikryukov/work/USD_build_23_11/include/pxr/base/tf/pyObjWrapper.h:37:
[build] In file included from /Users/ikryukov/work/USD_build_23_11/include/boost/functional/hash.hpp:6:
[build] /Users/ikryukov/work/USD_build_23_11/include/boost/container_hash/hash.hpp:132:33: error: no template named 'unary_function' in namespace 'std'; did you mean '__unary_function'?
[build]         struct hash_base : std::unary_function<T, std::size_t> {};
[build]                            ~~~~~^
[build] /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__functional/unary_function.h:46:1: note: '__unary_function' declared here
[build] using __unary_function = __unary_function_keep_layout_base<_Arg, _Result>;
[build] ^
[build] 1 error generated.

Apple clang version 15.0.0 (clang-1500.0.40.1)
Target: arm64-apple-darwin23.1.0

I can confirm that adding add_compile_definitions(BOOST_NO_CXX98_FUNCTION_BASE) to my make project helps.

[nvmkuruc]

The following PRs remove boost::hash from OpenUSD. They should be released in 24.02. Is cherry picking those commits an option for your 23.11 build?

#2785
#2765
#2764
#2763