melib: make Backendfolder::children return slice

melib/src/backends.rs

@@ -308,7 +308,7 @@ pub trait BackendFolder: Debug {
     fn path(&self) -> &str;
     fn change_name(&mut self, new_name: &str);
     fn clone(&self) -> Folder;
-    fn children(&self) -> &Vec<FolderHash>;
+    fn children(&self) -> &[FolderHash];
     fn parent(&self) -> Option<FolderHash>;
 
     fn permissions(&self) -> FolderPermissions;
@@ -338,7 +338,7 @@ impl BackendFolder for DummyFolder {
         folder_default()
     }
 
-    fn children(&self) -> &Vec<FolderHash> {
+    fn children(&self) -> &[FolderHash] {
         &self.v
     }
 

melib/src/backends/imap/folder.rs

@@ -50,7 +50,7 @@ impl BackendFolder for ImapFolder {
         self.name = s.to_string();
     }
 
-    fn children(&self) -> &Vec<FolderHash> {
+    fn children(&self) -> &[FolderHash] {
         &self.children
     }
 

melib/src/backends/maildir.rs

@@ -295,7 +295,7 @@ impl BackendFolder for MaildirFolder {
         self.name = s.to_string();
     }
 
-    fn children(&self) -> &Vec<FolderHash> {
+    fn children(&self) -> &[FolderHash] {
         &self.children
     }
 

melib/src/backends/mbox.rs

@@ -120,7 +120,7 @@ impl BackendFolder for MboxFolder {
         })
     }
 
-    fn children(&self) -> &Vec<FolderHash> {
+    fn children(&self) -> &[FolderHash] {
         &self.children
     }