feat: add calltoc

__ffi/calltoc/src/main.rs

@@ -0,0 +1,37 @@
+use std::ffi::{c_char, CStr};
+use std::ops::Deref;
+
+extern "C" {
+    fn hello() -> *const c_char;
+    fn goodbye(s: *const c_char);
+}
+
+struct Greeting {
+    message: *const c_char,
+}
+
+impl Drop for Greeting {
+    fn drop(&mut self) {
+        unsafe { goodbye(self.message); }
+    }
+}
+
+impl Greeting {
+    fn new() -> Greeting {
+        Greeting { message: unsafe { hello() } }
+    }
+}
+
+impl Deref for Greeting {
+    type Target = str;
+    fn deref<'a>(&'a self) -> &'a str {
+        let c_str = unsafe{ CStr::from_ptr(self.message) };
+        c_str.to_str().unwrap()
+    }
+}
+
+
+fn main() {
+    let greeting = Greeting::new();
+    println!("{}", greeting.deref());
+}