Slightly improve performance of builders

Builders would keep a `serde_json::Map<String, Value>`, which would
require re-creating owned strings for the same parameter multiple times
in some cases, depending on builder defaults and keying strategies.

This commit uses a `std::collections::HashMap<&'static str, Value>`
internally, and moves over values to a `serde_json::Map<String, Value>`
when it comes time to sending them to the appropriate `http` module
function.

This saves the number of heap-allocated string creations on most
builders, with specific performance increase on `builder::CreateMessage`
and `builder::CreateEmbed` & co.

2 files changed, 21 insertions, 13 deletions

diff --git a/src/model/guild/guild_id.rs b/src/model/guild/guild_id.rs
index efda6a8..2771fc8 100644
--- a/src/model/guild/guild_id.rs
+++ b/src/model/guild/guild_id.rs
@@ -5,11 +5,11 @@ use CACHE;
 #[cfg(feature = "model")]
 use builder::{EditGuild, EditMember, EditRole};
 #[cfg(feature = "model")]
-use http;
-#[cfg(feature = "model")]
 use internal::prelude::*;
 #[cfg(feature = "model")]
 use model::guild::BanOptions;
+#[cfg(feature = "model")]
+use {http, utils};
 
 #[cfg(feature = "model")]
 impl GuildId {
@@ -168,7 +168,9 @@ impl GuildId {
     /// [Manage Roles]: permissions/constant.MANAGE_ROLES.html
     #[inline]
     pub fn create_role<F: FnOnce(EditRole) -> EditRole>(&self, f: F) -> Result<Role> {
-        http::create_role(self.0, &f(EditRole::default()).0)
+        let map = utils::hashmap_to_json_map(f(EditRole::default()).0);
+
+        http::create_role(self.0, &map)
     }
 
     /// Deletes the current guild if the current account is the owner of the
@@ -229,7 +231,9 @@ impl GuildId {
     /// [Manage Guild]: permissions/constant.MANAGE_GUILD.html
     #[inline]
     pub fn edit<F: FnOnce(EditGuild) -> EditGuild>(&mut self, f: F) -> Result<PartialGuild> {
-        http::edit_guild(self.0, &f(EditGuild::default()).0)
+        let map = utils::hashmap_to_json_map(f(EditGuild::default()).0);
+
+        http::edit_guild(self.0, &map)
     }
 
     /// Edits an [`Emoji`]'s name in the guild.
@@ -266,7 +270,9 @@ impl GuildId {
     #[inline]
     pub fn edit_member<F, U>(&self, user_id: U, f: F) -> Result<()>
         where F: FnOnce(EditMember) -> EditMember, U: Into<UserId> {
-        http::edit_member(self.0, user_id.into().0, &f(EditMember::default()).0)
+        let map = utils::hashmap_to_json_map(f(EditMember::default()).0);
+
+        http::edit_member(self.0, user_id.into().0, &map)
     }
 
     /// Edits the current user's nickname for the guild.
@@ -300,7 +306,9 @@ impl GuildId {
     #[inline]
     pub fn edit_role<F, R>(&self, role_id: R, f: F) -> Result<Role>
         where F: FnOnce(EditRole) -> EditRole, R: Into<RoleId> {
-        http::edit_role(self.0, role_id.into().0, &f(EditRole::default()).0)
+        let map = utils::hashmap_to_json_map(f(EditRole::default()).0);
+
+        http::edit_role(self.0, role_id.into().0, &map)
     }
 
     /// Search the cache for the guild.
diff --git a/src/model/guild/member.rs b/src/model/guild/member.rs
index 90dca58..7420faa 100644
--- a/src/model/guild/member.rs
+++ b/src/model/guild/member.rs
@@ -6,15 +6,13 @@ use model::*;
 #[cfg(feature = "model")]
 use std::borrow::Cow;
 #[cfg(all(feature = "cache", feature = "model"))]
-use CACHE;
-#[cfg(all(feature = "cache", feature = "model"))]
 use internal::prelude::*;
-#[cfg(all(feature = "cache", feature = "model"))]
-use http;
 #[cfg(all(feature = "builder", feature = "cache", feature = "model"))]
 use builder::EditMember;
 #[cfg(all(feature = "cache", feature = "model", feature = "utils"))]
 use utils::Colour;
+#[cfg(all(feature = "cache", feature = "model"))]
+use {CACHE, http, utils};
 
 pub trait BanOptions {
     fn dmd(&self) -> u8 { 0 }
@@ -109,7 +107,8 @@ impl Member {
     pub fn add_roles(&mut self, role_ids: &[RoleId]) -> Result<()> {
         self.roles.extend_from_slice(role_ids);
 
-        let map = EditMember::default().roles(&self.roles).0;
+        let builder = EditMember::default().roles(&self.roles);
+        let map = utils::hashmap_to_json_map(builder.0);
 
         match http::edit_member(self.guild_id.0, self.user.read().id.0, &map) {
             Ok(()) => Ok(()),
@@ -227,7 +226,7 @@ impl Member {
     /// [`EditMember`]: ../builder/struct.EditMember.html
     #[cfg(feature = "cache")]
     pub fn edit<F: FnOnce(EditMember) -> EditMember>(&self, f: F) -> Result<()> {
-        let map = f(EditMember::default()).0;
+        let map = utils::hashmap_to_json_map(f(EditMember::default()).0);
 
         http::edit_member(self.guild_id.0, self.user.read().id.0, &map)
     }
@@ -361,7 +360,8 @@ impl Member {
     pub fn remove_roles(&mut self, role_ids: &[RoleId]) -> Result<()> {
         self.roles.retain(|r| !role_ids.contains(r));
 
-        let map = EditMember::default().roles(&self.roles).0;
+        let builder = EditMember::default().roles(&self.roles);
+        let map = utils::hashmap_to_json_map(builder.0);
 
         match http::edit_member(self.guild_id.0, self.user.read().id.0, &map) {
             Ok(()) => Ok(()),