Monthly Archives: April 2019

Type inference debate: a C++ culture phenomenon?

I read two C++ subreddit threads today on using the auto keyword. They’re both questions: the first one asks why certain people seem to dislike using type inference, while the second asks about what commonly taught guidelines should be considered bad practice. A few replies there mention auto.

This confuses me for more than one reason. The first is that I’m a big proponent of type inference. Having to work to tell a computer what it already knows is one of my pet peeves. I also believe that wanting to know the exact type of a variable is a, for lack of a better term, “development smell”, especially in typed languages with generics. I think that the possible operations on a type are what matters, and figuring out the exact type if needed is a tooling problem that is solved almost everywhere. If you don’t at least have “jump to definition” in your development environment, you should.

The other main source of confusion for me is why this debate seems restricted to the C++ community, at least according to my anectodal evidence. As far as I’m aware of, type inference is taken to be a good thing almost universally in Go, D, Rust, Haskell, et al. I don’t have statistics on this at all, but from what I’ve seen so far it seems to be the case. Why is that?

One reason might be change. As I learned reading Peopleware, humans aren’t too fond of it. C++ lacked type inference until C++11, and whoever learned it then might not like using auto now; it’s “weird”, so it must be bad. I’ve heard C programmers who “like” looping over a collection using an integer index and didn’t understand when I commented on their Python code asking them to please not do that. “Like” here means “this is what I’m used to”. Berating people for disliking change is definitely not the way forward, however. One must take their feelings into account if one wants to effect change. Another lesson learned from Peopleware: the problem is hardly ever technical.

Otherwise, I’m not sure. I’m constantly surprised by what other people find to be more or less readable when it comes to code. There are vocal opponents to operator overloading, for instance. I have no idea why.

What do you think? Where do you stand on auto?

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Boden, Flutter, React Native?

A while back I had an idea for a mobile app that I still might write. The main problems were finding the time and analysis paralysis: what do I write the project in?

I’ve done some Android development before using Qt, and it was a hassle. I’ve been told that JNI was made painful on purpose so that nobody would try to do it and I can see why. At least at the time the Android NDK had modern compilers compared to what my team was allowed to use for the rest of the codebase and it was my first taste of C++11 in production.

As much as I dislike the Apple ecosystem, it would be foolish to say the least to ignore iOS. Writing Java for the Android UI I can deal with (but wouldn’t be happy about), learning Objective C or Swift? That I’m not sure of. In any case, I don’t want to write UI code twice.

Since then, I’ve been meaning to look at Flutter, which seems to avoid most of the problems I would have to face otherwise. But that means learning Dart, which would be a significant sidetrack. Yesterday however, I learned on cppcast that there’s a C++ alternative called boden. On the one hand, I don’t have to learn a new language. On the other hand I have to write C++, with all the swordfights and seg faults that entails. Which leads me all the way back to analysis paralysis.

There’s also React Native and Xamarin, and probably a few other alternatives, but they all for reasons I can’t quite explain give me a bit of an allergic reaction.

I guess I’m going to have to bite the bullet and try one of these frameworks. Or all of them. Now to think of a tiny but not useless test project…

Build systems are stupid

Big complicated projects nearly always need a build system. They might be generating code. They might be compiling different branches depending on the platform or a build-time configuration option. They might turn on/off unity builds for C++.  For most simple projects however, build systems are stupid.

Let’s say you have a single C file. We need to tell the compiler the name of the file we want to compile, and the name of the resulting binary unless we’re happy with it being called a.out, which is unlikely:

gcc -Wall -Wextra -Werror -o foo foo.c

Maybe it’s the first commit in brand new repository and all you have is foo.c in there. Why am I telling the compiler what to build? What else would it build??

$ ls
$ gcc
gcc: fatal error: no input files
compilation terminated.

“Real projects don’t look like that!”. Ok:

$ ls
build include src 
$ ls src
foo.c main.c
$ ls include

I doubt any humans who have ever written C before would be confused as to how this project is supposed to be compiled. And yet, this is probably the simplest way I can come up with to tell the computer to do it properly:

CFLAGS ?= -Iinclude -Wall -Wextra -Werror -g

SRCS := $(shell find src -name *.c)
HDRS := $(shell find include -name *.h)
OBJS := $(subst src,build,$(subst .c,.o,$(SRCS)))

build/foo: $(OBJS)
	gcc -o $@ $^

build/%.o: src/%.c $(HDRS)
	gcc $(CFLAGS) -o $@ -c $<

Is there a better way than $(subst)? Probably. I don’t care. I was also too lazy to figure out dependencies so all source files depend on all headers. That’s a lot of lines of Makefile and all I wanted to specify were that source files are in src, headers are in include, binaries go inbuild, and that the compiler flags are -Wall -Wextra -Werror  -g. The first three are obvious from the existence and names of those directories, so there are 8 lines of code here to tell a computer what the compiler flags are. Robots: 1 Humans: 0.

CMake isn’t that much better:

cmake_minimum_required (VERSION 2.8.11)
project (foo)

add_executable(foo ${SRC_FILES})
target_include_directories(foo PRIVATE ${PROJECT_SOURCE_DIR}/include)

Robots: 2 Humans: 0.

I’ll probably get told off for using file(GLOB) because what I really should be doing is manually listing source files because reasons. Why would I have files in src if I don’t want them to be compiled? In what universe does it make sense for a person whose job it is to tell computers what to do so that they don’t have to do it themselves to tell a build system which files to build? In my opinion every new language should default to doing what Pony does. Running the compiler just builds everything in the current directory tree.

I also think that new languages should ship with a compiler-based build system, i.e. the compiler is the build system. The reason for that is that as a developer, I want to rebuild the minimum possible amount of code that is required after my edits to run my tests. The CMake solution above fails at this: the compiler calculates dependencies and automatically feeds it into the build system, but those dependencies are too coarse.

If I touch any header, all source files that #include it will be recompiled. This happens even if it’s an additive change, which by definition can’t affect any existing source files.  If I change a function’s signature that is only used in foo.c, well tough: I’ll have to wait until bar.c, baz.c and quux.c all get recompiled for the temerity of depending on different functions from the same header.

This problem is bad enough in C and C++ but actually gets worse for languages with modules: now every file is a “header”. Changes to the implementation trigger recompilations, because our build systems are too stupid to know any better. I can’t see how a good build system can be an external tool unless the compiler is a library, and even then it would be doing the same work twice since dependency calculations are better done while a module/translation unit is being compiled.

Taking it a step further, the whole concept of caring about files and modules is probably outdated anyway. Why not a Smalltalk-like environment? You make changes to the source and your “image” gets rebuilt in the background, one part of the AST at a time, automagically resolving and rebuilding dependencies (at the function level!).

Computers and build systems: what have you done for me lately?

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