Comment by manawy | Hacker News Reader

Comment by manawy | Hacker News Reader

Parent Full thread

I'm not sure what you mean by databases of systems and features...

I use CMake everyday and for me it's not a database but a set of modules. Each of this module will look for a particular thing. Some modules are better written than other but they all allow you to bypass them. Of course on obscure systems it will fail. That's why they are called obscure. But on systems following more or less the good practice, there will be no problem at all. On the others, you need to pass the specific path, but it will be true with autoconf too... no magic here...

Also in the doc, it is stated that if you rely on a specific flag/option/function then you need to test for it, and CMake gives you the tool to do it. That's a good practice everyone should follow.

But I agree, it's not always done. Like Autoconf, I guess it really depends on how well the developer understand the tool, and how much time he is ready to spend on it.

There's no magic, it's a complicated problem, with only complicated solutions. CMake is more attractive to me, because it allows me to do simple stuff easily, but more complicated operations are also possible.

> I'm not sure what you mean by databases of systems and features...

I didn't really mean a literal database. I meant stuff like this:

https://github.com/Kitware/CMake/blob/master/Modules/FindQt4...

This is pretty typical CMake. It's encoding that for a particular version of Qt, add a few more compilation flags. It's a "knowledge base" of Qt versions encoded as a CMake module.

The autoconf way would be to try to link a minimal program to Qt, and if it fails, try to see if adding more libraries makes the linking succeed.

Or this, for example:

https://github.com/Kitware/CMake/blob/master/Modules/FindOpe...

It is trying to account for two popular compilers on Windows but not with Cygwin. It's the whole chain of "if Windows, if cygwin, if mingw, if msvc" what I called a "database" above.

Doesn't clang work on Windows these days? What will this knowledge base do now? Shouldn't clang work almost like mingw? But because it misses the "if mingw" branch, code that probably would have worked for clang will be skipped over.

I'd argue that for Qt this approach makes sense because they provide a well defined API that they stick too. The developer can also ask for specific component if it just want them (like QT GUI, QT SVG...).

I agree that this is more problematic with less common, more buggy libs where the API keep changing, but in this case it's quite easy to check for specific files, specific functions, ...

All this assumptions have huge consequences in terms of velocity and ease of use.

For your second example, this does not test for the compiler but for the provider of the SSL library. Clang does not provided it, so it's not a problem.

But I get your point.

My counter-argument is that more flexibility is left to the developer to assume stuff. These assumptions make things easier in most cases. In corner cases, then you need to provide explicit values to the module so he can find what you need.

Reply on news.ycombinator.com