make say use Option

src/command/kill.rs

@@ -0,0 +1,17 @@
+#[derive(Default)]
+pub struct KillCommand {
+    target: Option<super::Selector>
+}
+
+impl KillCommand {
+    pub fn target(mut self, target: super::Selector) -> Self {
+        self.target = Some(target);
+        self
+    }
+
+    pub fn build(self) -> super::Command {
+        let target = self.target.unwrap_or(super::Selector::Executor);
+        let s = format!("kill {target}");
+        super::Command(s)
+    }
+}

src/command/list.rs

@@ -1,16 +1,16 @@
 #[derive(Default)]
 pub struct ListCommand {
-    uuids: bool
+    uuids: Option<bool>
 }
 
 impl ListCommand {
     pub fn uuids(mut self) -> Self {
-        self.uuids = true;
+        self.uuids = Some(true);
         self
     } 
 
     pub fn build(self) -> super::Command {
-        let uuids = self.uuids;
+        let uuids = self.uuids.unwrap_or(false);
         let mut s = format!("list");
         if uuids {
             s.push_str(" uuids");

src/command/mod.rs

@@ -1,7 +1,32 @@
+use std::fmt::Display;
+
 pub struct Command(String);
 
+pub enum Selector {
+    NearestPlayer, // @p
+    RandomPlayer, // @r
+    AllPlayers, // @a
+    AllEntities, // @e
+    Executor, // @s
+    NearestEntity // @n
+}
+
+impl Display for Selector {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::NearestPlayer => write!(f, "@p"),
+            Self::RandomPlayer => write!(f, "@r"),
+            Self::AllPlayers => write!(f, "@a"),
+            Self::AllEntities => write!(f, "@e"),
+            Self::Executor => write!(f, "@s"),
+            Self::NearestEntity => write!(f, "@n")
+        }
+    }
+}
+
 mod say;
 mod list;
+mod kill;
 
 impl Command {
     pub fn raw(cmd: &str) -> Self {

src/command/say.rs

@@ -1,16 +1,16 @@
 #[derive(Default)]
 pub struct SayCommand {
-    message: String
+    message: Option<String>
 }
 
 impl SayCommand {
     pub fn message(mut self, msg: impl Into<String>) -> Self {
-        self.message = msg.into();
+        self.message = Some(msg.into());
         self
     } 
 
     pub fn build(self) -> super::Command {
-        let message = self.message;
+        let message = self.message.unwrap_or("Hello, world!".to_string());
         let s = format!("say {message}");
         super::Command(s)
     }

src/lib.rs

@@ -2,4 +2,4 @@ mod client;
 pub use client::{RconClient, RconError, RconResult};
 
 mod command;
-pub use command::Command;
+pub use command::{Command, Selector};