Reintroduce macro for enum Display and FromStr impls.

src/call/mod.rs

@@ -26,3 +26,10 @@ pub enum SessionDescriptionType {
     #[serde(rename="offer")]
     Offer,
 }
+
+impl_enum! {
+    SessionDescriptionType {
+        Answer => "answer",
+        Offer => "offer",
+    }
+}

src/lib.rs

@@ -16,6 +16,8 @@ use serde::{Deserialize, Deserializer, Error as SerdeError, Serialize, Serialize
 use serde::de::Visitor;
 use serde_json::Value;
 
+#[macro_use] mod macros;
+
 pub mod call;
 pub mod presence;
 pub mod receipt;
@@ -24,6 +26,9 @@ pub mod stripped;
 pub mod tag;
 pub mod typing;
 
+/// An error when attempting to convert a string to an enum that only accepts certain values.
+pub struct ParseError;
+
 /// The type of an event.
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub enum EventType {

src/macros.rs

@@ -0,0 +1,24 @@
+macro_rules! impl_enum {
+    ($name:ident { $($variant:ident => $s:expr,)+ }) => {
+        impl ::std::fmt::Display for $name {
+            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
+                let variant = match *self {
+                    $($name::$variant => $s,)*
+                };
+
+                write!(f, "{}", variant)
+            }
+        }
+
+        impl ::std::str::FromStr for $name {
+            type Err = $crate::ParseError;
+
+            fn from_str(s: &str) -> Result<Self, Self::Err> {
+                match s {
+                    $($s => Ok($name::$variant),)*
+                    _ => Err($crate::ParseError),
+                }
+            }
+        }
+    }
+}

src/presence.rs

@@ -54,3 +54,11 @@ pub struct PresenceEventExtraContent {
     /// The unique identifier for the event.
     pub event_id: EventId,
 }
+
+impl_enum! {
+    PresenceState {
+        Offline => "offline",
+        Online => "online",
+        Unavailable => "unavailable",
+    }
+}

src/room/guest_access.rs

@@ -26,3 +26,10 @@ pub enum GuestAccess {
     #[serde(rename="forbidden")]
     Forbidden,
 }
+
+impl_enum! {
+    GuestAccess {
+        CanJoin => "can_join",
+        Forbidden => "forbidden",
+    }
+}

src/room/history_visibility.rs

@@ -38,3 +38,12 @@ pub enum HistoryVisibility {
     #[serde(rename="world_readable")]
     WorldReadable,
 }
+
+impl_enum! {
+    HistoryVisibility {
+        Invited => "invited",
+        Joined => "joined",
+        Shared => "shared",
+        WorldReadable => "world_readable",
+    }
+}

src/room/join_rules.rs

@@ -32,3 +32,12 @@ pub enum JoinRule {
     #[serde(rename="public")]
     Public,
 }
+
+impl_enum! {
+    JoinRule {
+        Invite => "invite",
+        Knock => "knock",
+        Private => "private",
+        Public => "public",
+    }
+}

src/room/member.rs

@@ -67,3 +67,13 @@ pub struct MemberEventExtraContent {
     #[serde(skip_serializing_if="Option::is_none")]
     pub invite_room_state: Option<Vec<StrippedState>>,
 }
+
+impl_enum! {
+    MembershipState {
+        Ban => "ban",
+        Invite => "invite",
+        Join => "join",
+        Knock => "knock",
+        Leave => "leave",
+    }
+}

src/room/message.rs

@@ -238,6 +238,19 @@ pub struct VideoInfo {
     pub w: Option<u64>,
 }
 
+impl_enum! {
+    MessageType {
+        Audio => "m.audio",
+        Emote => "m.emote",
+        File => "m.file",
+        Image => "m.image",
+        Location => "m.location",
+        Notice => "m.notice",
+        Text => "m.text",
+        Video => "m.video",
+    }
+}
+
 impl Serialize for MessageEventContent {
     fn serialize<S>(&self, serializer: &mut S) -> Result<(), S::Error> where S: Serializer {
         match *self {