example C extension

Author: johnno1962

Package.swift

@@ -0,0 +1,8 @@
+import PackageDescription
+
+let package = Package(
+    name: "Clibadder",
+    targets: [
+        Target(name: "Clibadder", dependencies: ["libadder"])
+    ]
+)

Sources/Clibadder/Clibadder.swift

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+import libadder
+protocol Addable {
+    func add(_ x: Int, _ y: Int) -> Int
+}
+
+public struct SimpleAdd: Addable {
+    func add(_ x: Int, _ y: Int) -> Int {
+        return libadder.add(x, y)
+    }
+}
+
+public struct StructAdd: Addable {
+    func add(_ x: Int, _ y: Int) -> Int {
+        let op = add_operation(x: x, y: y, result: 0)
+        let result = libadder.added(op)
+        return result.result;
+    }
+}
+
+public struct PointerAdd: Addable {
+    func add(_ x: Int, _ y: Int) -> Int {
+        var op = add_operation(x: x, y: y, result: 0)
+        libadder.adding(&op)
+        return op.result;
+    }
+}

Sources/libadder/include/libadder.h

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+// our struct to hold values
+typedef struct {
+    long x;
+    long y;
+    long result;
+} add_operation;
+
+// simple add method
+long add(long x, long y);
+// struct by value
+add_operation added(add_operation op);
+// pointer to struct
+void adding(add_operation *op);

Sources/libadder/libadder.c

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+#import "include/libadder.h"
+
+long add(long x, long y) {
+    return x + y;
+}
+
+add_operation added(add_operation op) {
+    add_operation result = {op.x, op.y, add(op.x, op.y)};
+    return result;
+}
+
+void adding(add_operation *op) {
+    op->result = add(op->x, op->y);
+}