feat: use trait to define builtins

Cargo.lock

@@ -169,10 +169,17 @@ dependencies = [
  "static_assertions",
 ]
 
+[[package]]
+name = "once_cell"
+version = "1.17.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6f61fba1741ea2b3d6a1e3178721804bb716a68a6aeba1149b5d52e3d464ea66"
+
 [[package]]
 name = "pmuw-project"
 version = "0.1.0"
 dependencies = [
+ "once_cell",
  "rustyline",
  "shlex",
 ]

Cargo.toml

@@ -4,5 +4,6 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
+once_cell = "1.17"
 rustyline = "10.1.0"
 shlex = "1.1"

src/builtins/cd.rs

@@ -1,8 +1,16 @@
+use crate::builtins::Builtin;
 use std::env::set_current_dir;
 
 use crate::error::ShellError;
 
-pub fn run(args: Vec<String>) -> Result<(), ShellError> {
-    set_current_dir(args.get(0).unwrap());
-    Ok(())
+pub struct Cd;
+
+impl Builtin for Cd {
+    fn execute(&mut self, args: Vec<String>) -> Result<(), ShellError> {
+        let Some(first) = args.get(0) else {
+            return Err(ShellError::ExecuteFailure("no argument given".to_string()))
+        };
+
+        set_current_dir(first).map_err(|e| ShellError::ExecuteFailure(e.to_string()))
+    }
 }

src/builtins/exit.rs

@@ -1,5 +1,10 @@
+use crate::builtins::Builtin;
 use crate::error::ShellError;
 
-pub fn run() -> Result<(), ShellError> {
+pub struct Exit;
+
+impl Builtin for Exit {
+    fn execute(&mut self, _: Vec<String>) -> Result<(), ShellError> {
         Err(ShellError::Exit)
     }
+}

src/builtins/mod.rs

@@ -1,18 +1,26 @@
 use crate::error::ShellError;
+use once_cell::unsync::Lazy;
 mod cd;
 mod exit;
 
-const BUILTINS: &[&str] = &["exit", "cd"];
+trait Builtin: Sync + Send {
+    fn execute(&mut self, args: Vec<String>) -> Result<(), ShellError>;
+}
+
+const BUILTINS: Lazy<Vec<(&str, Box<dyn Builtin>)>> =
+    Lazy::new(|| vec![("cd", Box::new(cd::Cd)), ("exit", Box::new(exit::Exit))]);
 
 pub fn is_builtin(keyword: &str) -> bool {
-    BUILTINS.contains(&keyword)
+    BUILTINS.iter().find(|(k, _)| k == &keyword).is_some()
 }
 
+#[allow(const_item_mutation)]
 pub fn execute_builtin(keyword: &str, args: Vec<String>) -> Result<(), ShellError> {
-    match keyword {
-        "exit" => exit::run()?,
-        "cd" => cd::run(args)?,
-        _ => {}
+    if let Some(builtin) = BUILTINS
+        .iter_mut()
+        .find_map(|(k, c)| if k == &keyword { Some(c) } else { None })
+    {
+        builtin.execute(args)?
     }
     Ok(())
 }