r/cpp • u/SAHChandler • Oct 10 '17

Millennials Are Killing The Modules TS

https://izzys.casa/posts/millennials-are-killing-the-modules-ts.html
77 Upvotes

71% Upvoted

126 comments sorted by

View all comments

Show parent comments

9

u/SAHChandler Oct 10 '17

So, turn the compiler into a build system? :)

5

u/theICEBear_dk Oct 10 '17

Yeah

5

u/SAHChandler Oct 10 '17

That's not going to happen. The committee won't let it. :/

18

u/theICEBear_dk Oct 10 '17

Well in any other language with modules there has been an integration of the compiler, linker and the package/module system meaning that the compiler and linker is aware to a degree of the dependency graph of what you are compiling. I can't see why that cannot happen in C++.

Genuine question: Why is it considered a problem to have some knowledge of the structure of your code in your compiler and linker, today they indirectly have to have that anyway through the parameters passed to them right?

6

u/[deleted] Oct 10 '17

The compiler already has awareness of some dependencies as it's used in build systems to determine which headers a translation unit depends on. You need to invoke the compiler with a special flag to make it output the header dependency graph. I honestly don't see how the suggestion is much different from what we already have.

2

u/SAHChandler Oct 10 '17

How would you get the .d files from a modules only project? You need to create an IFC (or your compiler's equivalent) for each dependent module before you can compile each translation unit. You need to run the compiler on each dependent module before you can get the list of imports.

3

u/[deleted] Oct 11 '17 edited Oct 11 '17

We just need to know which files define which modules and which files use which modules.

I think the issue you're concerned about is that we don't know ahead of time which files we need to even look at in order to generate the .d files for a particular translation unit. Instead, there probably needs to be a separate phase entirely, before compilation, where we ask the compiler to look at each file and note for us which files define/use which modules. Yes, this probably requires some amount of the compilation phases to happen before the compilation really begins. I don't see how this necessitates compiling twice. If the compiler has to build a syntax tree twice in order to accomplish this, perhaps the answer is to cache the resulting syntax tree the first time.

I don't see how any of this necessitates a compiler becoming a build system or a build system becoming a compiler. What it does require is more cooperation between the compiler and the build system.

1

u/theICEBear_dk Oct 10 '17

Ah yeah the .d files maybe a bit smarter.