redef fun compile_extern_method(block, m, ecc, mmodule)
	do
		var fc = new ExternCFunction(m, mmodule)
		fc.decls.add( block.location.as_line_pragma )
		fc.exprs.add( block.code )
		ecc.body_impl.add fc.to_writer
	end

	# We call C++ from C using 2 more files (_ffi.c and _ffi.cpp) and multiple generated functions:
	# 1. The standard C implementation function (___impl) expected by the common FFI
	# 2. The indirection function (___cpp_impl_mid) is a C function, called from C but implemented as `extern "C"` in C++
	# 3. The actual C++ implementation function (___cpp_impl)
	redef fun compile_extern_method(block, m, ecc, mmodule)
	do
		if mmodule.cpp_file == null then mmodule.cpp_file = new CPPCompilationUnit

		var mclass_type = m.parent.as(AClassdef).mclass.mclass_type
		var mproperty = m.mpropdef.mproperty

		# Signature of the indirection function implemented as `extern "C"` in C++
		var indirection_sig = mproperty.build_csignature(mclass_type, mmodule, "___cpp_impl_mid", long_signature, internal_call_context)

		## In C file (__ffi.c)

		# Declare the indirection function in C
		ecc.body_decl.add("{indirection_sig};\n")

		# Call the indirection function from C (___impl)
		var fc: CFunction = new ExternCFunction(m, mmodule)
		fc.exprs.add(mproperty.build_ccall(mclass_type, mmodule, "___cpp_impl_mid", long_signature, cpp_call_context, null))
		fc.exprs.add("\n")
		ecc.add_exported_function( fc )

		## In C++ file (__ffi.cpp)

		# Declare the indirection function in C++
		mmodule.cpp_file.header_decl.add("extern \"C\" \{\n")
		mmodule.cpp_file.header_decl.add("{indirection_sig};\n")
		mmodule.cpp_file.header_decl.add("\}\n")

		# Implement the indirection function as extern in C++
		# Will convert C arguments to C++ and call the C++ implementation function.
		fc = new CFunction(indirection_sig)
		if not mproperty.is_init then
			var param_name = "self"
			var type_name = to_cpp_call_context.name_mtype(mclass_type)
			if mclass_type.mclass.ftype isa ForeignCppType then
				fc.exprs.add("{type_name} {param_name}_for_cpp = static_cast<{type_name}>({param_name});\n")
			else
				fc.exprs.add("{type_name} {param_name}_for_cpp = {param_name};\n")
			end
		end
		for param in m.mpropdef.msignature.mparameters do
			var param_name = param.name
			var type_name = to_cpp_call_context.name_mtype(param.mtype)
			if mclass_type.mclass.ftype isa ForeignCppType then
				fc.exprs.add("{type_name} {param_name}_for_cpp = static_cast<{type_name}>({param_name});\n")
			else
				fc.exprs.add("{type_name} {param_name}_for_cpp = {param_name};\n")
			end
		end
		fc.exprs.add(mproperty.build_ccall(mclass_type, mmodule, "___cpp_impl", long_signature, cpp_call_context, "_for_cpp"))
		fc.exprs.add("\n")
		mmodule.cpp_file.add_exported_function(fc)

		# Custom C++, the body of the Nit C++ method is copied to its own C++ function
		var cpp_signature = mproperty.build_csignature(mclass_type, mmodule, "___cpp_impl", long_signature, cpp_call_context)
		fc = new CFunction(cpp_signature)
		fc.decls.add( block.location.as_line_pragma )
		fc.exprs.add( block.code )
		mmodule.cpp_file.add_local_function( fc )
	end

	redef fun compile_extern_method(block, m, ccu, mmodule)
	do
		ffi_ccu = ccu
		mmodule.ensure_java_files
		var java_file = mmodule.java_file
		assert java_file != null

		var mclass_type = m.parent.as(AClassdef).mclass.mclass_type
		var mmethodef = m.mpropdef
		var mproperty = m.mpropdef.mproperty

		# C function calling the Java method through JNI
		var fc = new ExternCFunction(m, mmodule)

		fc.exprs.add """
	jclass java_class;
	jmethodID java_meth_id;

	// retrieve the current JVM
	Sys sys = Pointer_sys(NULL);
	JNIEnv *nit_ffi_jni_env = Sys_jni_env(sys);

	// retrieve the implementation Java class
	java_class = Sys_load_jclass(sys, "{{{mmodule.impl_java_class_name}}}");
	if (java_class == NULL) {
		PRINT_ERROR("Nit FFI with Java error: failed to load class.\\n");
		(*nit_ffi_jni_env)->ExceptionDescribe(nit_ffi_jni_env);
		exit(1);
	}

	// register callbacks (only once per Nit module)
	if (!nit_ffi_with_java_registered_natives) nit_ffi_with_java_register_natives(nit_ffi_jni_env, java_class);
"""

		# Retrieve the Java implementation function id
		var java_fun_name = mproperty.build_cname(mclass_type, mmodule, "___java_impl", long_signature)
		var jni_format = mproperty.build_jni_format(mclass_type, mmodule)
		fc.exprs.add """
	// retreive the implementation static function
	java_meth_id = (*nit_ffi_jni_env)->GetStaticMethodID(nit_ffi_jni_env, java_class, "{{{java_fun_name}}}", "{{{jni_format}}}");
	if (java_meth_id == NULL) {
		PRINT_ERROR("Nit FFI with Java error: Java implementation not found.\\n");
		(*nit_ffi_jni_env)->ExceptionDescribe(nit_ffi_jni_env);
		exit(1);
	}
"""

		# Call the C Java implementation method from C
		var signature = mmethodef.msignature
		assert signature != null

		var jni_signature_alt
		var return_type
		var params = new Array[String]
		params.add "nit_ffi_jni_env"
		params.add "java_class"
		params.add "java_meth_id"

		if mproperty.is_init then
			jni_signature_alt = mclass_type.jni_signature_alt
			return_type = mclass_type
		else
			params.add to_java_call_context.cast_to(mclass_type, "self")
			if signature.return_mtype != null then
				var ret_mtype = signature.return_mtype
				ret_mtype = ret_mtype.resolve_for(mclass_type, mclass_type, mmodule, true)
				return_type = signature.return_mtype
				jni_signature_alt = return_type.jni_signature_alt
			else
				jni_signature_alt = "Void"
				return_type = null
			end
		end

		for p in signature.mparameters do
			var param_mtype = p.mtype
			param_mtype = param_mtype.resolve_for(mclass_type, mclass_type, mmodule, true)
			params.add(to_java_call_context.cast_to(param_mtype, p.name))
		end

		var cname = "(*nit_ffi_jni_env)->CallStatic{jni_signature_alt}Method"
		var ccall
		if return_type != null then
			ccall = "{return_type.jni_type} jni_res = {cname}({params.join(", ")});"
		else ccall = "{cname}({params.join(", ")});"

		fc.exprs.add """
	// execute implementation code
	{{{ccall}}}
	if ((*nit_ffi_jni_env)->ExceptionCheck(nit_ffi_jni_env)) {
		PRINT_ERROR("Nit FFI with Java error: Exception after call.\\n");
		(*nit_ffi_jni_env)->ExceptionDescribe(nit_ffi_jni_env);
		exit(1);
	}

	(*nit_ffi_jni_env)->DeleteLocalRef(nit_ffi_jni_env, java_class);
"""

		if return_type != null then
			fc.exprs.add "\treturn {to_java_call_context.cast_from(return_type, "jni_res")};"
		end

		ccu.add_exported_function( fc )

		# Java implementation function in Java
		var java_csig = mproperty.build_csignature(mclass_type, mmodule, "___java_impl", long_signature, java_call_context)
		mmodule.java_file.class_content.add """
	public static {{{java_csig}}} {
		// from Nit FII at: {{{block.location}}}
		{{{block.code}}}
	}
"""

		mmodule.callbacks_used_from_java.join m.foreign_callbacks
	end

	redef fun compile_extern_method(block, m, ecc, mmodule)
	do
		if mmodule.objc_file == null then mmodule.objc_file = new ObjCCompilationUnit

		var mpropdef = m.mpropdef
		var recv_mtype = mpropdef.mclassdef.bound_mtype
		var csignature = mpropdef.mproperty.build_csignature(
			recv_mtype, mmodule, "___impl", long_signature, from_objc_call_context)

		var fc = new CFunction(csignature)
		fc.decls.add block.location.as_line_pragma
		fc.exprs.add block.code
		mmodule.objc_file.add_exported_function fc
	end