Merge pull request #6865 from vjpai/stylin

Doc Fixit: Introduce C++ style guide

doc/c-style-guide.md

@@ -11,7 +11,7 @@ General
 
 - Layout rules are defined by clang-format, and all code should be passed through
   clang-format. A (docker-based) script to do so is included in 
-  tools/distrib/clang_format_code.sh.
+  [tools/distrib/clang\_format\_code.sh] (../tools/distrib/clang_format_code.sh).
 
 Header Files
 ------------

doc/cpp-style-guide.md

+GRPC C++ STYLE GUIDE
+=====================
+
+Background
+----------
+
+Here we document style rules for C++ usage in the gRPC C++ bindings
+and tests.
+
+General
+-------
+
+- The majority of gRPC's C++ requirements are drawn from the [Google C++ style
+guide] (https://google.github.io/styleguide/cppguide.html)
+   - However, gRPC has some additional requirements to maintain
+     [portability] (#portability)
+- As in C, layout rules are defined by clang-format, and all code
+should be passed through clang-format. A (docker-based) script to do
+so is included in [tools/distrib/clang\_format\_code.sh]
+(../tools/distrib/clang_format_code.sh).
+
+<a name="portability"></a>
+Portability Restrictions
+-------------------
+
+gRPC supports a large number of compilers, ranging from those that are
+missing many key C++11 features to those that have quite detailed
+analysis. As a result, gRPC compiles with a high level of warnings and
+treat all warnings as errors. gRPC also forbids the use of some common
+C++11 constructs. Here are some guidelines, to be extended as needed:
+- Do not use range-based for. Expressions of the form
+  ```c
+  for (auto& i: vec) {
+    // code
+  }
+  ```
+  
+  are not allowed and should be replaced with code such as
+  ```c
+  for (auto it = vec.begin; it != vec.end(); it++) {
+    auto& i = *it;
+    // code
+  }
+  ```
+  
+- Do not use lambda of any kind (no capture, explicit capture, or
+default capture). Other C++ functional features such as
+`std::function` or `std::bind` are allowed
+- Do not use brace-list initializers.
+- Do not compare a pointer to `nullptr` . This is because gcc 4.4
+  does not support `nullptr` directly and gRPC implements a subset of
+  its features in [include/grpc++/impl/codegen/config.h]
+  (../include/grpc++/impl/codegen/config.h). Instead, pointers should
+  be checked for validity using their implicit conversion to `bool`.
+  In other words, use `if (p)` rather than `if (p != nullptr)`
+- Do not use `final` or `override` as these are not supported by some
+  compilers. Instead use `GRPC_FINAL` and `GRPC_OVERRIDE` . These
+  compile down to the traditional C++ forms for compilers that support
+  them but are just elided if the compiler does not support those features.
+- In the [include] (../../../tree/master/include/grpc++) and [src]
+  (../../../tree/master/src/cpp) directory trees, you should also not
+  use certain STL objects like `std::mutex`, `std::lock_guard`,
+  `std::unique_lock`, `std::nullptr`, `std::thread` . Instead, use
+  `grpc::mutex`, `grpc::lock_guard`, etc., which are gRPC
+  implementations of the prominent features of these objects that are
+  not always available. You can use the `std` versions of those in  [test]
+  (../../../tree/master/test/cpp)
+- Similarly, in the same directories, do not use `std::chrono` unless
+  it is guarded by `#ifndef GRPC_CXX0X_NO_CHRONO` . For platforms that
+  lack`std::chrono,` there is a C-language timer called gpr_timespec that can
+  be used instead.
+- `std::unique_ptr` must be used with extreme care in any kind of
+  collection. For example `vector<std::unique_ptr>` does not work in
+  gcc 4.4 if the vector is constructed to its full size at
+  initialization but does work if elements are added to the vector
+  using functions like `push_back`. `map` and other pair-based
+  collections do not work with `unique_ptr` under gcc 4.4. The issue
+  is that many of these collection implementations assume a copy
+  constructor
+  to be available.
+- Don't use `std::this_thread` . Use `gpr_sleep_until` for sleeping a thread.
+- [Some adjacent character combinations cause problems]
+  (https://en.wikipedia.org/wiki/Digraphs_and_trigraphs#C). If declaring a
+  template against some class relative to the global namespace,
+  `<::name` will be non-portable. Separate the `<` from the `:` and use `< ::name`.