[Spice-devel] Coding style and naming conventions for C++

[Frediano Ziglio]

> 
> Hi Lukáš,
> 
> 
> In the specific case of the streaming agent, I believe it matters
> for instant productivity that the code follow a style that does not
> require additional thinking on Frediano’s part. So if Frediano likes
> it, it’s fine by me, otherwise don’t care.
> 
> Also, rather than invent a style, I’d rather adopt an standard coding
> style, e.g. Google’s. And then use clang-format to enforce all the
> machine-enforceable parts of it.
> 
> 
> Regards,
> Christophe
> 
> PS: Some comments on your suggestions anyway…
> 
> > On 29 Jan 2018, at 15:19, Lukáš Hrázký <lhrazky at redhat.com> wrote:
> > 
> > Hello everybody,
> > 
> > I'd like to discuss a few things about the coding style for C++ in
> > Spice (looking at the streaming agent atm).
> > 
> > Trying to keep this short and concise.
> > 
> > 
> > 1. Method names
> > Currently the method names are in CamelCase throughout the streaming
> > agent. Methods are basically functions attached to a class, I suggest
> > we use snake_case to be consistent with the function names.
> > 
> > It's rather confusing when you see a call like SomeObject(), which
> > looks like a constructor, but you actually find out it's a method call
> > from another method of the same class.
> 
> Naming a method with a name that can also be a class is always
> ambiguous, CamelCase or not. Is color() a method or an ctor?
> So DeCamelCaseIfication not a solution to that problem.
> 
> BTW, CamelCase is so frequent in C++ that it often can be used to identify
> code as being C++ as opposed to plain C. To wit: LLVM, WebKit, Qt, etc.
> 
> > 
> > 
> > ;2. Namespace names
> > Although not standard (you may have different experience), usually
> > namespaces are lowercase in C++.
> 
> By that token, so do classes (in all of the standard library).
> But it’s generally not true outside of the standard library.
> 
> > Also, they are hierarchical, I suggest
> > we use that and in streaming agent we change the namespace like so:
> > 
> > SpiceStreamingAgent -> spice::streamingagent
> > 
> > or (imho better):
> > SpiceStreamingAgent -> spice::streaming_agent
> > 
> > And stick to this scheme, i.e. lowercase and toplevel namespace
> > 'spice', inside it a namespace of the component.
> 
> Not against the idea, but two levels of namespace for
> 2000 LOCs seems a tad bit overkill…
> 

Always better to plan big :-)
I don't think is overkilling.

> 
> > 
> > 
> > 3. Namespace coding style
> > 
> > a) Let's not use `using namespace ...` ever even in .cpp files (see
> > i.e. [1]). In streaming agent we have at the beginning of every .cpp:
> > 
> > using namespace std;
> > using namespace SpiceStreamingAgent;
> 
> Again, 2000 lines of code, unlikely to grow much.
> Google’s rule applies to their mega-projects, but for the agent,
> I think that “using namespace” makes the code leaner.
> 

I think here the distinction is usage and implementation.

1) implementation. If you want to implement a class my_namespace::MyClass you
  probably want to use:

#include "my_class_header.hpp"

namespace my_namespace {

MyClass::MyClass(...)
{
  ...
}

...

}

2) usage. Here you want to use the class my_namespace::MyClass, you probably
  want:

#include "my_class_header.hpp"

using namespace my_namespace;

...

   auto *my_obj = new MyClass(...);



I think does it make sense. About the using in 2) depends on how much the code
is using the namespace or personal preference.

> > 
> > For namespace std, "std::" is not a long prefix, clearly expresses the
> > identifier is from the standard library and AFAIK most C++ projects use
> > it this way.
> > 
> > For namespace SpiceStreamingAgent, I didn't even know it worked for
> > definition of symbols in the namespace. First time I see it, it is very
> > unusual. see b).
> > 
> > b) Let's keep the following coding style for namespaces, i.e. for
> > streaming agent:
> > 
> > namespace spice {
> > namespace streaming_agent {
> > 
> > THE_CODE
> > 
> > }} // namespace spice::streaming_agent
> 
> Not too enthusiastic about }}
> 

weird too, but with comment is more understandable (I would say
required).

> > 
> > 
> > We should add the guidelines to the website next to the C coding style,
> > but I have no intention to be exhaustive (see [1] for how long it can
> > be), let's add important cases as they come up and just use common
> > sense, keep the style of the local code and codereview to keep things
> > in check?
> 
> Let’s first share our preference on existing styles to see if we agree on
> anything…
> As for me, I have a slight preference for the LLVM coding style, but I made
> modifications in my own clang-format files.
> 

The problem here is that we already have plenty of other code, not clear
if/how we should be coherent with it (considering also that's almost C but
considering that and the fact that C++ is really C friendly I can think
that we could include and use lot of existing C code).

> 
> Regards
> Christophe
> 
> 
> > 
> > Lukas
> > 
> > 
> > [1] https://google.github.io/styleguide/cppguide.html#Namespaces

Frediano