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.

1 files changed, 16 insertions, 2 deletions

diff --git a/src/utils/mod.rs b/src/utils/mod.rs
index c6d27c3..5783c41 100644
--- a/src/utils/mod.rs
+++ b/src/utils/mod.rs
@@ -13,18 +13,32 @@ pub use self::message_builder::{Content, ContentModifier, MessageBuilder};
 pub use super::builder;
 
 use base64;
+use internal::prelude::*;
+use model::{EmojiId, EmojiIdentifier};
+use std::collections::HashMap;
 use std::ffi::OsStr;
 use std::fs::File;
+use std::hash::Hash;
 use std::io::Read;
 use std::path::Path;
-use internal::prelude::*;
-use model::{EmojiId, EmojiIdentifier};
 
 #[cfg(feature = "cache")]
 use cache::Cache;
 #[cfg(feature = "cache")]
 use CACHE;
 
+/// Converts a HashMap into a final `serde_json::Map` representation.
+pub fn hashmap_to_json_map<T>(map: HashMap<T, Value>) -> Map<String, Value>
+    where T: Eq + Hash + ToString {
+    let mut json_map = Map::new();
+
+    for (key, value) in map.into_iter() {
+        json_map.insert(key.to_string(), value);
+    }
+
+    json_map
+}
+
 /// Determines if a name is NSFW.
 ///
 /// This checks that the name is either `"nsfw"` or, for names longer than that,