perf: use slices instead of cloning

src/email_client.rs

@@ -34,11 +34,11 @@ impl EmailClient {
         // TODO: use `reqwest::Url::join` and change `base_url`'s type from `String` to `reqwest::Url`
         let url = format!("{}/email", self.base_url);
         let request_body = SendEmailRequest {
-            from: self.sender.as_ref().to_owned(),
-            to: recipient.as_ref().to_owned(),
-            subject: subject.to_owned(),
-            html_body: html_content.to_owned(),
-            text_body: text_content.to_owned(),
+            from: self.sender.as_ref(),
+            to: recipient.as_ref(),
+            subject,
+            html_body: html_content,
+            text_body: text_content,
         };
         let _builder = self
             .http_client
@@ -55,12 +55,12 @@ impl EmailClient {
 }
 #[derive(serde::Serialize)]
 #[serde(rename_all = "PascalCase")]
-struct SendEmailRequest {
-    from: String,
-    to: String,
-    subject: String,
-    html_body: String,
-    text_body: String,
+struct SendEmailRequest<'a> {
+    from: &'a str,
+    to: &'a str,
+    subject: &'a str,
+    html_body: &'a str,
+    text_body: &'a str,
 }
 
 #[cfg(test)]