Add low level code style description (#1736)

Add code_style.rst document that describes C++ formatting and naming conventions

Signed-off-by: Efimov Alexander <a.efimov@samsung.com>

diff --git a/contrib/nnc/doc/codestyle.rst b/contrib/nnc/doc/codestyle.rst
new file mode 100644 (file)
index 0000000..5624893
--- /dev/null
+++ b/contrib/nnc/doc/codestyle.rst
@@ -0,0 +1,182 @@
+Low-level issues
+================
+
+Naming styles:
+--------------
+
+- `snake_case` - name starts with lower case, words divided by underscore
+- `CamelCase` - name starts with Upper case, words starts with Upper case, no divider
+- `camelCase` - name starts with lower case, words(except first) starts with Upper case, no divider
+- `_camelCase` - name starts with underscore, first word starts with lower case, other with Upper case, no divider
+- `ALL_UPPER` - all characters in Upper case, words divided by underscore
+
+General indentations and limits:
+--------------------------------
+
+- Line of code should be no longer than 100 characters(including comments)
+- Opening brace should stay on the same line with corresponding statement
+- Stick **\*** and **&** in variable declaration to type name: **Shape* s;**
+- Do not declare multiple pointer or reference variables separated by commas
+- Block contents of **{}** should be indented with 2 spaces, excluding:
+
+  + access modifiers in classes
+  + namespaces
+  + initializer lists
+  + **case** contents
+
+- No tabs allowed, only spaces
+
+Directories and file names:
+---------------------------
+
+- Directory names should be in snake_case
+- File names should be in CamelCase(SomeFile.cpp, SomeFile.h)
+
+Namespaces:
+-----------
+
+- Namespaces names should be in came_case, one word names are prefered: **cli**, **mir**, **some_long_namespace**
+- Use unnamed namespaces to hide all non-interface functions and classes of translation unit
+- No **using namespace** or **using namespace::classname** in headers
+- Namespace contents are not indented
+
+Enum & Macros:
+--------------
+
+- Enum(class and non-class) names should be in `CamelCase`
+- Elements of class enum should be in `camelCase`
+- Non-class enum elements should be in `ALL_UPPER` case
+- Macro names should be in `ALL_UPPER` case
+
+Functions & Methods:
+--------------------
+
+- Global functions and method names should be in `camelCase`
+- Virtual methods should be marked with **override** in derived class
+
+Global variables:
+-----------------
+
+- Global variables(static && non static) should be in `camelCase` (including constant data)
+
+Local variables:
+----------------
+
+- Names should be in snake_case
+
+Classes & Structures & Unions:
+------------------------------
+
+- Names of classes, structures and unions should be in `CamelCase`
+- Private(and protected) data should be in `_camelCase`
+- Public data should be in `camelCase`
+- Classes should have only one section of each type(public, private)
+- Access modifiers(public, private, protected) should not be indented relative to class declaration
+- Sections should go in order: public, protected, private
+- Methods go first, then data
+- If class has constructors they should be first defined methods
+- If class has destructor it should go after constructors
+
+.. code-block:: c++
+
+    class AnotherFoo : public Foo {
+    public:
+      explicit AnotherFoo() = default;
+      ~AnotherFoo() = default;
+
+      /**
+       * @brief Definitely does something
+      */
+      void doSomething() noexcept {
+        //...//
+      }
+    protected:
+    private:
+      int _foosInt;
+    }
+
+Templates:
+----------
+
+- Add space before angle brackets in template declaration and no spaces inside: **template <int>**
+- Do not add space before angle brackets in template instantiation and no spaces inside: **foo<12321>()**
+- Use **typename** instead of **class** in template parameters
+
+Control flow contructions:
+--------------------------
+
+- Function call should have no spaces around parentheses and have spaces after commas: **someFunc(arg1, arg2);**
+- **if**, **while**, **for** should have space after reserved word: **if (cond)** **while (cond)** **for (cond)**
+- **switch** should always have **default** case, if all cases are checked and **default** is redundant, place **assert(false)** in it
+- Avoid redundant braces inside switch **case**
+- **case** labels should be indented by 2 spaces relative to **switch**
+- Code in **code** section sould be indented by 2 spaces relative to corresponding **case**
+- Do not use non-empty cases with fallthrough( i.e. always add **break** )
+- Braces after **if**, **for**, **while** are optional if condition and predicate code are one lined
+- If **if** operator has else branch it's content should be one lined too to apply "no braces" rule:
+ 
+.. code-block:: c++
+
+   if (cond)
+     a = this;
+   else
+     b = that;
+
+
+.. code-block:: c++
+
+   switch(cond) {
+     case 0:
+     case 1:
+       doThis();
+       break;
+     case 2:
+       doThat();
+       break;
+     case 3: {
+       int x = 42;
+       useX(x);
+     }
+     default:
+       assert(false);
+   }
+
+
+Comments:
+---------
+
+- Function, methods(except trivial getters and setters), classes, structures, enums, should be commented in described doxygen format.
+- All mentioned entities should have **@brief** field, exception is getters, they could define **@return** instead
+- Functions have to describe their arguments(**@param**), template arguments(**@tparam**), return value if non-void(**@return**), what kinds of exceptions could be thrown(**@throws**)
+- One line comments starts with ///
+- Multiline comments should start on a second line, all lines start from *****, text separated from ***** with whitespace and goes like this:
+
+.. code-block:: c++
+
+  /**
+   * @brief some method that does something
+   * @param arg some input data
+   *            continue arg explanation on second line
+   * @throws some exceptions
+   *         continue explanation of throws
+   *
+   * Detailed description
+   */
+
+Type aliases:
+-------------
+
+- Use **using** instead of **typedef**
+- Aliases for basic types should have names in `snake_case`: **using axis_t = int32_t;**
+- Aliases for user-defined types should have names in `CamelCase`: **using Shape = nnc::mir::Shape;**
+
+Misc:
+-----
+
+- No spaces around braces in initializer lists, spaces after commas: **{1, 2, 3}**
+- No spaces around square brackets in arrays: **int a[5];** **arr[53] = 1;**
+- Declare methods as const if they do not change the object
+- Declare objects and pointers with const modifier if possible
+- Always add spaces around assignment operators(**=**, **+=**, etc): **a = 32;**
+- Add spaces around operators reasonably, do not add spaces around operators if you want to group operations without parentheses: **res = a*b + c*d;**
+- Add **noexcept** specifier if function does not throw