readability improvement on executor (#2615)

src/core/executor.rs

@@ -41,16 +41,12 @@ impl Executor {
     ///
     /// Regardless of the executor (`SingleThread` or `ThreadPool`), panics in the task
     /// will propagate to the caller.
-    pub fn map<
+    pub fn map<A, R, F>(&self, f: F, args: impl Iterator<Item = A>) -> crate::Result<Vec<R>>
+    where
         A: Send,
         R: Send,
-        AIterator: Iterator<Item = A>,
         F: Sized + Sync + Fn(A) -> crate::Result<R>,
-    >(
-        &self,
-        f: F,
-        args: AIterator,
-    ) -> crate::Result<Vec<R>> {
+    {
         match self {
             Executor::SingleThread => args.map(f).collect::<crate::Result<_>>(),
             Executor::ThreadPool(pool) => {