2 files changed, 11 insertions, 5 deletions
diff --git a/src/args.rs b/src/args.rs
index 8647ea7..10b8fea 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -26,7 +26,14 @@ use crate::suggestion::SuggestionsBuilder;
 /// The parsing context of a command.
 pub struct CommandContext<'i, S, E>(::std::marker::PhantomData<(&'i str, S, E)>);
 
-/// An argument parser.
+/// An argument parser/validator.
+///
+/// Note: Iosonism requires arguments to be `Send + Sync`, but for ease when
+/// implementing generic argument types, those bounds are not reflected in this
+/// trait. Nevertheless, Iosonism doesn't itself use threads, so a [workaround]
+/// can be used if one needs non-`Send + Sync` argument types.
+///
+/// [workaround]: https://users.rust-lang.org/t/how-to-check-send-at-runtime-similar-to-how-refcell-checks-borrowing-at-runtime/68269
 ///
 /// # Type params
 ///
@@ -86,7 +93,7 @@ pub trait ArgumentType<S, E> {
 }
 
 /// Wrapper around `ArgumentType`, but with `Any`.
-pub(crate) trait ArgumentTypeAny<S, E> {
+pub(crate) trait ArgumentTypeAny<S, E>: Send + Sync {
     /// Parses an argument of this type, returning the parsed argument.
     fn parse<'i>(
         &self,
@@ -104,7 +111,7 @@ pub(crate) trait ArgumentTypeAny<S, E> {
     fn get_examples(&self) -> Cow<'static, [&str]>;
 }
 
-impl<T: ArgumentType<S, E>, S, E> ArgumentTypeAny<S, E> for T {
+impl<T: ArgumentType<S, E> + Send + Sync, S, E> ArgumentTypeAny<S, E> for T {
     fn parse<'i>(
         &self,
         reader: &mut Cursor<&'i str>,
diff --git a/src/tree.rs b/src/tree.rs
index daac8d3..71243be 100644
--- a/src/tree.rs
+++ b/src/tree.rs
@@ -3,7 +3,6 @@
 // Licensed under the MIT license.
 // Documentation and comments licensed under CC BY-SA 4.0.
 
-#![allow(dead_code, unused_imports)] // for now
 //! Command syntax tree.
 
 use ::std::borrow::Cow;
@@ -75,7 +74,7 @@ impl<T, S, E> CommandNode<T, S, E> {
     }
 
     /// Creates a new argument node.
-    pub fn argument<A: ArgumentType<S, E> + 'static>(
+    pub fn argument<A: ArgumentType<S, E> + 'static + Send + Sync>(
         name: Cow<'static, str>,
         command: Option<Command<T, S, E>>,
         argument: A,