Use FnOnce in Command::perform

... and revert `FnMut` usage.

futures/src/command.rs

@@ -41,7 +41,7 @@ impl<T> Command<T> {
     }
 
     /// Applies a transformation to the result of a [`Command`].
-    pub fn map<A>(self, mut f: impl FnMut(T) -> A) -> Command<A>
+    pub fn map<A>(self, f: impl Fn(T) -> A) -> Command<A>
     where
         T: 'static,
     {

native/src/clipboard.rs

@@ -30,7 +30,7 @@ impl Clipboard for Null {
 /// [`Command`]: crate::Command
 pub enum Action<T> {
     /// Read the clipboard and produce `T` with the result.
-    Read(Box<dyn FnOnce(Option<String>) -> T>),
+    Read(Box<dyn Fn(Option<String>) -> T>),
 
     /// Write the given contents to the clipboard.
     Write(String),
@@ -40,7 +40,7 @@ impl<T> Action<T> {
     /// Maps the output of a clipboard [`Action`] using the provided closure.
     pub fn map<A>(
         self,
-        f: impl FnOnce(T) -> A + 'static + MaybeSend + Sync,
+        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
     ) -> Action<A>
     where
         T: 'static,

native/src/command.rs

@@ -56,7 +56,7 @@ impl<T> Command<T> {
     /// Applies a transformation to the result of a [`Command`].
     pub fn map<A>(
         self,
-        f: impl FnMut(T) -> A + 'static + MaybeSend + Sync + Clone,
+        f: impl Fn(T) -> A + 'static + MaybeSend + Sync + Clone,
     ) -> Command<A>
     where
         T: 'static,

native/src/command/action.rs

@@ -35,7 +35,7 @@ impl<T> Action<T> {
     /// [`Command`]: crate::Command
     pub fn map<A>(
         self,
-        f: impl FnMut(T) -> A + 'static + MaybeSend + Sync,
+        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
     ) -> Action<A>
     where
         A: 'static,

native/src/system/action.rs

@@ -9,15 +9,15 @@ pub enum Action<T> {
     QueryInformation(Box<dyn Closure<T>>),
 }
 
-pub trait Closure<T>: FnOnce(system::Information) -> T + MaybeSend {}
+pub trait Closure<T>: Fn(system::Information) -> T + MaybeSend {}
 
-impl<T, O> Closure<O> for T where T: FnOnce(system::Information) -> O + MaybeSend {}
+impl<T, O> Closure<O> for T where T: Fn(system::Information) -> O + MaybeSend {}
 
 impl<T> Action<T> {
     /// Maps the output of a system [`Action`] using the provided closure.
     pub fn map<A>(
         self,
-        f: impl FnOnce(T) -> A + 'static + MaybeSend + Sync,
+        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
     ) -> Action<A>
     where
         T: 'static,

native/src/widget/action.rs

@@ -16,7 +16,7 @@ impl<T> Action<T> {
     /// Maps the output of an [`Action`] using the given function.
     pub fn map<A>(
         self,
-        f: impl FnMut(T) -> A + 'static + MaybeSend + Sync,
+        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
     ) -> Action<A>
     where
         T: 'static,
@@ -37,7 +37,7 @@ impl<T> Action<T> {
 #[allow(missing_debug_implementations)]
 struct Map<A, B> {
     operation: Box<dyn Operation<A>>,
-    f: Box<dyn FnMut(A) -> B>,
+    f: Box<dyn Fn(A) -> B>,
 }
 
 impl<A, B> Operation<B> for Map<A, B>
@@ -52,7 +52,7 @@ where
     ) {
         struct MapRef<'a, A, B> {
             operation: &'a mut dyn Operation<A>,
-            f: &'a mut dyn FnMut(A) -> B,
+            f: &'a dyn Fn(A) -> B,
         }
 
         impl<'a, A, B> Operation<B> for MapRef<'a, A, B> {