add lifecycle str

single_file_tests/lifecycle_str.rs

@@ -0,0 +1,12 @@
+
+
+fn main() {
+    let a = string_to_a_str(&"hello world!");
+    println!("{}", a);
+}
+
+// SAFE? may these codes cause memory leak?
+fn string_to_a_str(s: &str) -> &'static str {
+    Box::leak(s.to_owned().into_boxed_str())
+}
+