Есть много причин заниматься конверсией управляемых языков в нативные: это прежде всего производительность, но также защита от реверс-инжиниринга, поддержка аппаратных технологий или каких-то специфичных платформ. В этом докладе мы посмотрим на пример построения конвертера из C# в C++ и те нюансы, которые встречаются при решении этой задачи

1. Dmitri Nesteruk
JetBrains

2. Managed language = C#, Java, D etc.
GC (garbage collector), Unicode, …
Unmanaged language
Something that compiles to native code
More control, less safety
C/C++, VHDL, etc.

3. Performance
Stop-the-world GC
Low-level control (e.g., SIMD)
Collections (containers), multithreading
Defense against reverse-engineering
C#, Java are easy to decompile
Hardware support
CUDA, Xeon Phi
Portability (surprise!)
Sudden desire to write everything in С++

4. Lex the source code
Build AST
Resolve symbols
Traverse the tree, translating it to a different
language
Perfect translation is (of course) impossible

5. Translate syntax with fidelity
Fill the gaps in what’s missing
Replace equivalent constructs
List<>  vector<>
Handle cases where 1-to-1
mapping is impossible

6. Integral types
Use types from <cstdint>
int int32_t, byte  uint8_t, etc.
float/double as-is
Extended precision types (System.Decimal)
Need external libs 
Slightly different init rules

7. Unicode 
Most LoB apps do not absolutely require Unicode (nice to
have)
Relatively safe option:
string  std::wstring
char  wchar_t
Slightly more careless option: string/char
A completely safe solution has to allow strings to be nullptr
I.e., you either use char* or option<string>
Expensive, tedious, just use myString.empty()
Unicode in source (identifiers, literals, …) won’t work

8. class Person
{
string name;
int age;
}
class Person {
std::string name;
int32_t age;
public:
Person();
};

9. Managed languages
Give types default values
Allow initialization right in the declaration
In both cases, initialization happens in the
(generated) ctor
In C++, types don’t have default values. So we
are forced to make a constructor ourselves

10. Property = field+getter+setter
Can be read or write-only
Can be automatic
Name of field not specified
explicitly
Offers no benefit over a field in C++
Can have an inline initializer
More ctor abuse 
Two options here
GetXxx/SetXxx (safe, tedious)
__declspec(property)
(not C++ standard, but nicer)
int age;
public int Age
{
get { return age; }
set { age = value; }
}
// automatic
public int Age
{ get; set; }

11. __declspec(property(get = GetAge, put = PutAge))
int Age;
int GetAge() const { return age; }
void PutAge(int value) { … }
// later
Person p;
p.Age = 123; // calls PutAge()

12. Used in many places, e.g.:
Handling UI interactions
Property change notifications
C++ doesn’t have them
Boost.Signals
Tricky since event subscription is done with +=
And unsubscription with −=

13. template <typename T> class
INotifyPropertyChanged
{
public:
signal<void(const T*, string)>
PropertyChanged;
};

14. class Player : public INotifyPropertyChanged<Player>
{
int age;
public:
__declspec(property(get = GetAge, put = PutAge)) int Age;
int GetAge() const { return age; }
void PutAge(int value)
{
if (value == age) return;
PropertyChanged(this, "Age"); // oops, a string! (macro?)
age = value;
}

15. “The big problem”
GC  non-GC translation
Store everything as shared_ptr
Replace every `new` with make_shared
Detecting use-cases for make_unique very
difficult
Circular references (weak_ptr<>?)

16. References require#includes
Need a list of typeheader for STL etc.
Circular references may need forward
declarations
Header groupings (at namespace or folder
level)
Very tricky internal consistency (topological sort)
Also a good idea for IDEs

17. Type translation is (relatively) easy
int  int32_t
List<T>  vector<T>
Function call translation is harder
List.Add()  vector.emplace_back(), but…
Value vs ref. stuff

18. We need two converters
One for .H files
Another for .CPP files (implementation)
The option of doing everything inline isn’t
considered
There are situations where 100% inlining doesn’t
work

20. Naming convention
Clean Unicode handling
Automated API mapping

21. Questions?
dn@jetbrains.com
@dnesteruk
Come to the JB booth! (R#C++, CLion)