using the module file

src/example_3/.gitignore

@@ -0,0 +1,15 @@
+.dub
+docs.json
+__dummy.html
+docs/
+/example_3
+example_3.so
+example_3.dylib
+example_3.dll
+example_3.a
+example_3.lib
+example_3-test-*
+*.exe
+*.o
+*.obj
+*.lst

src/example_3/dub.json

@@ -0,0 +1,10 @@
+{
+	"authors": [
+		"alexander"
+	],
+	"copyright": "Copyright © 2021, alexander",
+	"description": "Основы работы с функциями",
+	"license": "proprietary",
+	"name": "example_3",
+    "targetPath": "bin"
+}

src/example_3/source/app.d

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+import std.stdio;
+import fun_;
+
+void main()
+{
+    uint a = 1;
+    double b = 2;
+    fun(a, b);
+    writeln(a, ' ', b);
+}

src/example_3/source/fun.d

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+module fun_;
+
+void fun(ref uint x, double y)
+{
+    x = 42;
+    y = 3.14;
+}