A C/C++ interop library for the Nim programming language.

Similar to the nimline library, this library allows one to interop with C/C++ code without having to generate wrappers with tools like nimterop. Unlike nimline, cinterop does not depend on Nim's experimental dotOperators feature and relies only on Nim's macro system to generate code.

• Provides convenience macros to declare C/C++ types and functions (decls.nim).
• Converts a subset of Nim to its syntactical equivalent in C/C++ without requiring forward declarations for all types and functions involved in the expression (exprs.nim).

See tests for examples of most features. This section provides an incomplete summary of the core functionality.

Say you have the following C++ class:

// simple.hpp

class CppClass1
{
public:
    int field1 = 1;

    int method1(int arg)
    {
        return 1 + arg;
    }
};

You simply need to declare the C++ type and the source file it resides in:

# simple.nim

csource "simple.hpp":
  type CppClass1* = object of CClass

and then you can access the fields and methods of that type:

# main.nim

var instance1 = CppClass1.init()

echo cexpr[cint]^instance1.field1 # prints "1"

cexpr[cint]^instance1.field1 = 2

echo cexpr[cint]^instance1.method1(instance1.field1) # prints "3"

Notice that cexpr[T]^ indicates the return type T of the whole expression, and only needs to be used at the beginning. This means that types for members do not need to be declared, as long as the type of the variable whose members are accessed is known.

Nim requires that the result of a function call with a return type must be used, so if the result of a method is to be discarded, one can use the cexpr^ invocation, which is shorthand for cexpr[void]^:

cexpr^instance1.method1(0)

If the type of a return value does not need to be known but is used in an operation, one can use the cauto^ invocation like so:

cauto^instance1.field1 += 2

To simplify the mechanics of cexpr[T]^, it is required on both sides of a binary operation if both sides are C/C++ expressions:

cexpr[cint]^instance1.field1 += cexpr[cint]^instance1.field1

cauto^instance1.field1 += cexpr[cint]^instance1.field1 # same as above

cauto^instance1.field1 += cauto^instance1.field1 # same as above

This project is maintained during my free time, and serves as a tool for a game engine I am writing after work hours. Contributions are welcome, and will merge them immediately if they serve to keep the project robust, simple, and maintainable.

Cheers and happy coding! 🍺