undefined | Better HN

0 pointsMereInterest4y ago0 comments

> I don't agree. I usually don't care so much when a particular feature was introduced into a language

I care very much when a feature was introduced into a language, because maintaining compatibility with earlier versions of the language determines what features may be used. If I'm working on a library that needs to be compatible with C++03, then that means avoiding smart pointers and rvalues. If I'm working on a library that needs to be compatible with C++11, then I need to write my own make_unique(). If I'm working on a library that needs to be compatible with C++14, then I need to avoid using structured bindings.

If a project allows breaking backwards compatibility, then SemVer is a great way to put that information front and center. If a project considers backwards compatibility to be a given, then there's no point in having a constant value hanging out in front of the version number.

> I mostly care whether or not code written assuming version X can be compiled with version Y of the compiler.

Semantic versioning can only tell that for the case where X < Y (old code on new compiler). In order to determine it for X > Y (new code on old compiler), you need to know when features were introduced.

0 comments

klabb34y ago

> In order to determine it for X > Y (new code on old compiler), you need to know when features were introduced.

I think this is a deliberate reduction of dimensionality. Go says that you don't need to worry (for long) about this case, because the toolchain must be updated regularly - and promises that it will be as pain free as possible. This simplifies for the Go team, for library authors, and library users in most cases, at the expense of maintaining a recent toolchain.

Not saying this tradeoff is for everyone, and I've never used C++ professionally so I'm probably ignorant. But are you saying it's common with production projects that use a compiler from 2003 or earlier? What's the use case?

grumpyprole4y ago

> But are you saying it's common with production projects that use a compiler from 2003 or earlier? What's the use case?

Modern C++ compilers are not necessarily available on all platforms. For example, Solaris, AIX or old RedHat versions. Go doesn't have this problem yet, but it will.

sobkas4y ago

> Not saying this tradeoff is for everyone, and I've never used C++ professionally so I'm probably ignorant. But are you saying it's common with production projects that use a compiler from 2003 or earlier? What's the use case?

Let's start with the fact that newer doesn't mean better. With already deployed compiler you have tested it and know that it works good enough (code it generates, bugs you have workarounds for, etc). Where with new compiler you are on step one. You must do work again.

Or vendors just support particular version they have patched.

Or you are scared of GPL3.

MereInterestOP4y ago

The first difference is that there isn't just a single compiler, but rather a standard that gets implemented by different compiler vendors. It's gotten better since then, but typically it would be a while between the updated standard being released and the standard being supported by most compilers. (And even then, some compilers might not support everything in the same way. For example, two-phase lookup was added in C++03, but MSVC didn't correctly handle it until 2017 [0].)

The second difference is that the C++ compiler may be tightly coupled to the operating system, and the glibc version used by the operating system. Go avoids this by statically compiling everything, but that comes with its own mess of security problems. (e.g. When HeartBleed came out, the only update needed was for libopenssl.so. If a similar issue occurred in statically compiled code, every single executable that used the library would need to be updated.) So in many cases, in order to support an OS, you need to support the OS-provided compiler version [1].

As an example, physics labs, because that's where I have some experience. Labs tend to be pretty conservative about OS upgrades, because nobody wants to hear that the expensive equipment can't be run because somebody changes the OS. So, "Scientific Linux" is frequently used, based on RHEL, and used up until the tail end of the life-cycle. RHEL6 was in production use until Dec. of 2020, and is still in extended support. It provides gcc 4.4, which was released in 2009. Now, gcc 4.4 did support some parts of early drafts of C++11 (optimistically known at the time as C++0x), but didn't have full support due to lack of a time machine.

So when I was writing a library for use in data analysis, I needed to know the language and stdlib feature support in a compiler released a decade earlier, and typically stay within the features of the standard from almost two decades earlier.

[0] https://devblogs.microsoft.com/cppblog/two-phase-name-lookup...

[1] You can have non-OS compilers, but then you may need to recompile all of your dependencies rather using the package manager's version, keep track of separate glibc versions using RPATH or LD_LIBRARY_PATH, and make sure to distribute those alongside your library. It's not hard for a single program, but it's a big step to ask users of a library to make.

j / k navigate · click thread line to collapse