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0 pointslelanthran2y ago0 comments

> What is great about header files?

One great thing - it's nice to have an interface[1] which already has tooling to let other languages use your private, hidden and compiled implementation.

If those C++ libraries that almost all of Python scientific work is built on had used modules[2] (or something similar) instead of headers, interfacing Python to those libraries would have been an immense effort.

Even with modules existing now, if you're writing something core and foundational in C++, it's not getting adopted like Numpy, BLAS, etc unless you also provide header files.

And that's just Python. Think of all the other languages that rely on performance critical code written in C++, and used with a C-only interface.

[1] Of course, your interface can't be a C++ interface either, so there's that.

[2] If modules were around at the time.

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dagmx2y ago

Headers are a really bad interface IMHO. Yes there’s tooling, but they require your headers be very very specific. Any deviance can break that tooling, so you’re either lucky in what you can bind or are writing to a very strict spec.

Modules on the other hand are more strict and would likely have made the job of writing language bindings easier and more predictable.

I’m not sure I agree with your logic about NumPy etc. You seem to be conflating technology limitations with policy ones. They could most certainly use modules too , since they exist in the compiled space anyway. They won’t because they make certain compiler compatibility guarantees but that’s a conflict of interests not of technical quality.

In general your argument feels a bit “older is better due to legacy support”. That would preclude almost any advancement in the space as well, because any new language feature (even just a keyword) would break all your examples above equally too.

lelanthranOP2y ago

> Modules on the other hand are more strict and would likely have made the job of writing language bindings easier and more predictable.

There's two ways for tooling like swig to work with modules:

1. Read the compiled module and generate the stubs to call into it.

2. Read the source code for the module and generate the stubs for it.

Which of those, do you think, is easier than reading C (not C++) header files?

dagmx2y ago

Reading the module information would be significantly easier. (which is not something swig can do today since swig hasn’t been updated in a while )

Parsing code to define an API is horribly fragile. A single macro or unknown keyword can break it. Hence why you had to specify C not C++ headers.

Having a statically defined metadata like C++ modules do would have greatly simplified binding generation

mardifoufs2y ago

That's interesting! Why would modules make it harder to interface with c++ from python ? Is it because the header files are a direct interface to the functions? How hard would it be to do the same from modules, would it just require tooling to support modules rather than directly provided header files?

(I just realized that I don't completely understand how exactly the new modules work, so I have some further reading to do! )

lelanthranOP2y ago

> Why would modules make it harder to interface with c++ from python ? Is it because the header files are a direct interface to the functions?

Well, they're simpler, they're text, and the tooling already exists (I use swig all the time to automatically make C functions and symbols available to Java and Python. Some Lisps as well).

The reason the tooling exists, is because they are simple, and they are text. Looking at the C++ module definition, it's unclear to me[1] that similar tooling for C++ modules will ever be possible.

As long as the most popular languages (Python, Java, etc) rely on a C header file for inter-call interoperability, header files aren't going away. No one wants to manually write the interface into a C++ library by hand.

[1] I'm no C++ expert though - the problems I see with modules includes things like lack of a standard to grab the interface from the compiled module, complexity of C++ to determine the interface from the actual source code, etc.

nicoburns2y ago

> Well, they're simpler, they're text, and the tooling already exists (I use swig all the time to automatically make C functions and symbols available to Java and Python. Some Lisps as well). > The reason the tooling exists, is because they are simple, and they are text. Looking at the C++ module definition, it's unclear to me[1] that similar tooling for C++ modules will ever be possible.

Perhaps there's something specific about C++'s module design that makes this difficult, but Rust has modules and has similar tooling to enable you to automatically generate bindings to other languages (including Python and Java).

Rusky2y ago

Really there's nothing stopping tooling like swig (or a C++ compiler for that matter) from processing module interfaces as text, just like headers. The language spec for modules doesn't require (or even really talk about) compiling them to any kind of binary or intermediate format.

Rather, the language spec aspect of modules is about symbol visibility and collisions. In terms that interop cares about, moving a declaration into a module just adjusts its name mangling, without changing much else about e.g. its presence in the object file.

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dagmx2y ago

Modules on the other hand are more strict and would likely have made the job of writing language bindings easier and more predictable.

lelanthranOP2y ago

> Modules on the other hand are more strict and would likely have made the job of writing language bindings easier and more predictable.

There's two ways for tooling like swig to work with modules:

1. Read the compiled module and generate the stubs to call into it.

2. Read the source code for the module and generate the stubs for it.

Which of those, do you think, is easier than reading C (not C++) header files?

dagmx2y ago

Reading the module information would be significantly easier. (which is not something swig can do today since swig hasn’t been updated in a while )

Parsing code to define an API is horribly fragile. A single macro or unknown keyword can break it. Hence why you had to specify C not C++ headers.

Having a statically defined metadata like C++ modules do would have greatly simplified binding generation

mardifoufs2y ago

(I just realized that I don't completely understand how exactly the new modules work, so I have some further reading to do! )

lelanthranOP2y ago

> Why would modules make it harder to interface with c++ from python ? Is it because the header files are a direct interface to the functions?

Well, they're simpler, they're text, and the tooling already exists (I use swig all the time to automatically make C functions and symbols available to Java and Python. Some Lisps as well).

nicoburns2y ago

Rusky2y ago

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