Further generic-ify `reaction_users` `after` param

Further generic-ify the `after` parameter on the `reaction_users` method
of the following structs:

- `ChannelId`
- `Group`
- `GuildChannel`
- `Message`
- `Channel`
- `GuildChannel`

Do this by changing the `U` trait bound from `Into<UserId>` to
`Into<Option<UserId>>`.

This resolves problems determining types when passing `None` as the
argument, as reported in #247.

6 files changed, 52 insertions, 49 deletions

diff --git a/src/model/channel/channel_id.rs b/src/model/channel/channel_id.rs
index 8ebdf2a..7093dfb 100644
--- a/src/model/channel/channel_id.rs
+++ b/src/model/channel/channel_id.rs
@@ -358,12 +358,13 @@ impl ChannelId {
     /// [`User`]: struct.User.html
     /// [Read Message History]: permissions/constant.READ_MESSAGE_HISTORY.html
     pub fn reaction_users<M, R, U>(&self,
-                                   message_id: M,
-                                   reaction_type: R,
-                                   limit: Option<u8>,
-                                   after: Option<U>)
-                                   -> Result<Vec<User>>
-        where M: Into<MessageId>, R: Into<ReactionType>, U: Into<UserId> {
+        message_id: M,
+        reaction_type: R,
+        limit: Option<u8>,
+        after: U,
+    ) -> Result<Vec<User>> where M: Into<MessageId>,
+                                 R: Into<ReactionType>,
+                                 U: Into<Option<UserId>> {
         let limit = limit.map_or(50, |x| if x > 100 { 100 } else { x });
 
         http::get_reaction_users(
@@ -371,7 +372,7 @@ impl ChannelId {
             message_id.into().0,
             &reaction_type.into(),
             limit,
-            after.map(|u| u.into().0),
+            after.into().map(|x| x.0),
         )
     }
 
diff --git a/src/model/channel/group.rs b/src/model/channel/group.rs
index 4a4070a..69e9cc7 100644
--- a/src/model/channel/group.rs
+++ b/src/model/channel/group.rs
@@ -238,15 +238,16 @@ impl Group {
     /// [`User`]: struct.User.html
     /// [Read Message History]: permissions/constant.READ_MESSAGE_HISTORY.html
     #[inline]
-    pub fn reaction_users<M, R, U>(&self,
-                                   message_id: M,
-                                   reaction_type: R,
-                                   limit: Option<u8>,
-                                   after: Option<U>)
-                                   -> Result<Vec<User>>
-        where M: Into<MessageId>, R: Into<ReactionType>, U: Into<UserId> {
-        self.channel_id
-            .reaction_users(message_id, reaction_type, limit, after)
+    pub fn reaction_users<M, R, U>(
+        &self,
+        message_id: M,
+        reaction_type: R,
+        limit: Option<u8>,
+        after: U,
+    ) -> Result<Vec<User>> where M: Into<MessageId>,
+                                 R: Into<ReactionType>,
+                                 U: Into<Option<UserId>> {
+        self.channel_id.reaction_users(message_id, reaction_type, limit, after)
     }
 
     /// Removes a recipient from the group. If the recipient is already not in
diff --git a/src/model/channel/guild_channel.rs b/src/model/channel/guild_channel.rs
index 4d729ea..3653cb6 100644
--- a/src/model/channel/guild_channel.rs
+++ b/src/model/channel/guild_channel.rs
@@ -531,15 +531,16 @@ impl GuildChannel {
     /// [`Message`]: struct.Message.html
     /// [`User`]: struct.User.html
     /// [Read Message History]: permissions/constant.READ_MESSAGE_HISTORY.html
-    pub fn reaction_users<M, R, U>(&self,
-                                   message_id: M,
-                                   reaction_type: R,
-                                   limit: Option<u8>,
-                                   after: Option<U>)
-                                   -> Result<Vec<User>>
-        where M: Into<MessageId>, R: Into<ReactionType>, U: Into<UserId> {
-        self.id
-            .reaction_users(message_id, reaction_type, limit, after)
+    pub fn reaction_users<M, R, U>(
+        &self,
+        message_id: M,
+        reaction_type: R,
+        limit: Option<u8>,
+        after: U,
+    ) -> Result<Vec<User>> where M: Into<MessageId>,
+                                 R: Into<ReactionType>,
+                                 U: Into<Option<UserId>> {
+        self.id.reaction_users(message_id, reaction_type, limit, after)
     }
 
     /// Sends a message with just the given message content in the channel.
diff --git a/src/model/channel/message.rs b/src/model/channel/message.rs
index 1bb55ab..f3834bd 100644
--- a/src/model/channel/message.rs
+++ b/src/model/channel/message.rs
@@ -313,14 +313,14 @@ impl Message {
     /// [`User`]: struct.User.html
     /// [Read Message History]: permissions/constant.READ_MESSAGE_HISTORY.html
     #[inline]
-    pub fn reaction_users<R, U>(&self,
-                                reaction_type: R,
-                                limit: Option<u8>,
-                                after: Option<U>)
-                                -> Result<Vec<User>>
-        where R: Into<ReactionType>, U: Into<UserId> {
-        self.channel_id
-            .reaction_users(self.id, reaction_type, limit, after)
+    pub fn reaction_users<R, U>(
+        &self,
+        reaction_type: R,
+        limit: Option<u8>,
+        after: U,
+    ) -> Result<Vec<User>> where R: Into<ReactionType>,
+                                 U: Into<Option<UserId>> {
+        self.channel_id.reaction_users(self.id, reaction_type, limit, after)
     }
 
     /// Returns the associated `Guild` for the message if one is in the cache.
diff --git a/src/model/channel/mod.rs b/src/model/channel/mod.rs
index 00fc7f6..1a6bcd5 100644
--- a/src/model/channel/mod.rs
+++ b/src/model/channel/mod.rs
@@ -371,14 +371,14 @@ impl Channel {
     #[deprecated(since = "0.4.2", note = "Use the inner channel's method")]
     #[inline]
     pub fn reaction_users<M, R, U>(&self,
-                                   message_id: M,
-                                   reaction_type: R,
-                                   limit: Option<u8>,
-                                   after: Option<U>)
-                                   -> Result<Vec<User>>
-        where M: Into<MessageId>, R: Into<ReactionType>, U: Into<UserId> {
-        self.id()
-            .reaction_users(message_id, reaction_type, limit, after)
+        message_id: M,
+        reaction_type: R,
+        limit: Option<u8>,
+        after: U,
+    ) -> Result<Vec<User>> where M: Into<MessageId>,
+                                 R: Into<ReactionType>,
+                                 U: Into<Option<UserId>> {
+        self.id().reaction_users(message_id, reaction_type, limit, after)
     }
 
     /// Retrieves the Id of the inner [`Group`], [`GuildChannel`], or
diff --git a/src/model/channel/private_channel.rs b/src/model/channel/private_channel.rs
index 877fa13..39dcac3 100644
--- a/src/model/channel/private_channel.rs
+++ b/src/model/channel/private_channel.rs
@@ -189,14 +189,14 @@ impl PrivateChannel {
     /// [Read Message History]: permissions/constant.READ_MESSAGE_HISTORY.html
     #[inline]
     pub fn reaction_users<M, R, U>(&self,
-                                   message_id: M,
-                                   reaction_type: R,
-                                   limit: Option<u8>,
-                                   after: Option<U>)
-                                   -> Result<Vec<User>>
-        where M: Into<MessageId>, R: Into<ReactionType>, U: Into<UserId> {
-        self.id
-            .reaction_users(message_id, reaction_type, limit, after)
+        message_id: M,
+        reaction_type: R,
+        limit: Option<u8>,
+        after: U,
+    ) -> Result<Vec<User>> where M: Into<MessageId>,
+                                 R: Into<ReactionType>,
+                                 U: Into<Option<UserId>> {
+        self.id.reaction_users(message_id, reaction_type, limit, after)
     }
 
     /// Pins a [`Message`] to the channel.