add lazy_static

lazy_static/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "lazy_static"
+version = "0.1.0"
+authors = ["Hatter Jiang <jht5945@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+lazy_static = "1.4.0"

lazy_static/src/main.rs

@@ -0,0 +1,10 @@
+#[macro_use]
+extern crate lazy_static;
+
+lazy_static! {
+    static ref USER_HOME: Option<String> = std::env::var("HOME").ok();
+}
+
+fn main() {
+    println!("User home: {:?}", *USER_HOME);
+}