This module provides a macro that helps to define C++ classes from Nim.
import cppclass
cppclass X:
public:
a: int
proc `X`(a: int = 1, b: int = 2, c: int = 3) =
(this[]).a = a
(this[]).b = b
(this[]).c = c
proc get(): int =
var
a = (this[]).a
b = (this[]).b
c = (this[]).c
return a + b + c
protected:
b: int
private:
c: int
var x: X
echo x.get()The class is emitted to the generated code by using {.emit.}. All the member functions are exported to C++ and imported back, so they can be used both in C++ and Nim. However, constructors and destructors are not imported, please import them by yourself.
import cppclass
cppclass Foo:
protected:
n: cint
public:
proc `Foo`(n: cint) =
this.n = n
proc get(): cint =
this.n
proc initFoo(n: cint): Foo {.importcpp: "Foo(@)", constructor.}
{.emit: "#include <iostream>".}
proc main =
var f1 = initFoo(10)
echo f1.get()
{.emit: """
Foo f2(20);
std::cout << f2.get() << std::endl;
""".}
main()Operators can also be defined, but only those valid in C++. Whether valid is checked by the C++ compiler. They will be transformed into C++ operators. Both `+` and `operator+` have the same meaning.
import cppclass
cppclass Bar:
protected:
v: uint8
public:
proc store(n: cint) =
this.v = uint8(n)
proc `+`(k: cint): cint =
cint(this.v) + k
{.emit: "#include <iostream>".}
proc main =
{.emit: """
Bar b;
b.store(4);
std::cout << b + 5 << std::endl;
""".}
main()Inheritance is supported, but only from one parent.
import cppclass
cppclass A:
protected:
a: cint = 1
cppclass B(A):
public:
b: cint
proc get(): cint =
this.a
var foo: B
echo foo.get()In the above example, B inherits from A. The mode is default to private. This can be changed by using some pragma-like syntax.
import cppclass
cppclass A:
private:
a: int
public:
proc get(): int =
this.a
proc store(a: int) =
this.a = a
cppclass B(A {.public.}):
public:
b: int
var foo: B
foo.store(2)
echo foo.get()-
Generic parameters are not supported, as well as nested classes.
-
Like in C++, the variable
thisis aptrto the object that uses the member function. -
Do not use
static[T]orlent Tas parameter or return type. -
A class can have GC'ed members (
ref,seq, ...), but they must bepublicand initialized withwasMoved. They should be destroyed properly. -
If a field (member) is not initialized, its value is undefined.
-
A class can not be exported because the emitted code is invisible from other modules.