diff --git a/src/authenticator.rs b/src/authenticator.rs
index 6c21771..1beaddb 100644
--- a/src/authenticator.rs
+++ b/src/authenticator.rs
@@ -159,7 +159,7 @@ where
             client: self.client,
             token_getter: self.token_getter,
             store: self.store,
-            delegate: delegate,
+            delegate,
         }
     }
 
@@ -217,15 +217,15 @@ where
                     match rr {
                         RefreshResult::Error(ref e) => {
                             delegate.token_refresh_failed(
-                                format!("{}", e.description().to_string()),
-                                &Some("the request has likely timed out".to_string()),
+                                e.description(),
+                                Some("the request has likely timed out"),
                             );
                             return Err(RequestError::Refresh(rr));
                         }
                         RefreshResult::RefreshError(ref s, ref ss) => {
                             delegate.token_refresh_failed(
-                                format!("{} {}", s, ss.clone().map(|s| format!("({})", s)).unwrap_or("".to_string())),
-                                &Some("the refresh token is likely invalid and your authorization has been revoked".to_string()),
+                                &format!("{}{}", s, ss.as_ref().map(|s| format!(" ({})", s)).unwrap_or_else(String::new)),
+                                Some("the refresh token is likely invalid and your authorization has been revoked"),
                                 );
                             return Err(RequestError::Refresh(rr));
                         }
diff --git a/src/authenticator_delegate.rs b/src/authenticator_delegate.rs
index 245cc54..ad3b37c 100644
--- a/src/authenticator_delegate.rs
+++ b/src/authenticator_delegate.rs
@@ -95,7 +95,7 @@ pub trait AuthenticatorDelegate: Clone + Send + Sync {
     /// Called if we could not acquire a refresh token for a reason possibly specified
     /// by the server.
     /// This call is made for the delegate's information only.
-    fn token_refresh_failed<S: AsRef<str>>(&self, error: S, error_description: &Option<String>) {
+    fn token_refresh_failed(&self, error: &str, error_description: Option<&str>) {
         {
             let _ = error;
         }
diff --git a/src/device.rs b/src/device.rs
index a5bbb60..8afc1f3 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -12,7 +12,7 @@ use url::form_urlencoded;
 use crate::authenticator_delegate::{DefaultFlowDelegate, FlowDelegate, PollInformation, Retry};
 use crate::types::{ApplicationSecret, GetToken, JsonErrorOr, PollError, RequestError, Token};
 
-pub const GOOGLE_DEVICE_CODE_URL: &'static str = "https://accounts.google.com/o/oauth2/device/code";
+pub const GOOGLE_DEVICE_CODE_URL: &str = "https://accounts.google.com/o/oauth2/device/code";
 
 /// Implements the [Oauth2 Device Flow](https://developers.google.com/youtube/v3/guides/authentication#devices)
 /// It operates in two steps:
@@ -215,7 +215,7 @@ where
         let resp = client
             .request(req)
             .await
-            .map_err(|e| RequestError::ClientError(e))?;
+            .map_err(RequestError::ClientError)?;
         // This return type is defined in https://tools.ietf.org/html/draft-ietf-oauth-device-flow-15#section-3.2
         // The alias is present as Google use a non-standard name for verification_uri.
         // According to the standard interval is optional, however, all tested implementations provide it.
@@ -294,12 +294,12 @@ where
         let res = client
             .request(request)
             .await
-            .map_err(|e| PollError::HttpError(e))?;
+            .map_err(PollError::HttpError)?;
         let body = res
             .into_body()
             .try_concat()
             .await
-            .map_err(|e| PollError::HttpError(e))?;
+            .map_err(PollError::HttpError)?;
         #[derive(Deserialize)]
         struct JsonError {
             error: String,
diff --git a/src/installed.rs b/src/installed.rs
index 88c90c0..8928261 100644
--- a/src/installed.rs
+++ b/src/installed.rs
@@ -19,7 +19,7 @@ use url::percent_encoding::{percent_encode, QUERY_ENCODE_SET};
 use crate::authenticator_delegate::{DefaultFlowDelegate, FlowDelegate};
 use crate::types::{ApplicationSecret, GetToken, JsonErrorOr, RequestError, Token};
 
-const OOB_REDIRECT_URI: &'static str = "urn:ietf:wg:oauth:2.0:oob";
+const OOB_REDIRECT_URI: &str = "urn:ietf:wg:oauth:2.0:oob";
 
 /// Assembles a URL to request an authorization token (with user interaction).
 /// Note that the redirect_uri here has to be either None or some variation of
@@ -39,9 +39,9 @@ where
     url.push_str(auth_uri);
     vec![
         format!("?scope={}", scopes_string),
-        format!("&access_type=offline"),
+        "&access_type=offline".to_string(),
         format!("&redirect_uri={}", redirect_uri.unwrap_or(OOB_REDIRECT_URI)),
-        format!("&response_type=code"),
+        "&response_type=code".to_string(),
         format!("&client_id={}", client_id),
     ]
     .into_iter()
@@ -258,12 +258,12 @@ where
             .client
             .request(request)
             .await
-            .map_err(|e| RequestError::ClientError(e))?;
+            .map_err(RequestError::ClientError)?;
         let body = resp
             .into_body()
             .try_concat()
             .await
-            .map_err(|e| RequestError::ClientError(e))?;
+            .map_err(RequestError::ClientError)?;
 
         #[derive(Deserialize)]
         struct JSONTokenResponse {
@@ -295,7 +295,7 @@ where
     }
 
     /// Sends the authorization code to the provider in order to obtain access and refresh tokens.
-    fn request_token<'a>(
+    fn request_token(
         appsecret: &ApplicationSecret,
         authcode: &str,
         custom_redirect_uri: Option<&str>,
@@ -318,11 +318,10 @@ where
             ])
             .finish();
 
-        let request = hyper::Request::post(&appsecret.token_uri)
+        hyper::Request::post(&appsecret.token_uri)
             .header(header::CONTENT_TYPE, "application/x-www-form-urlencoded")
             .body(hyper::Body::from(body))
-            .unwrap(); // TODO: error check
-        request
+            .unwrap() // TODO: error check
     }
 }
 
diff --git a/src/service_account.rs b/src/service_account.rs
index b2c93aa..545d7f5 100644
--- a/src/service_account.rs
+++ b/src/service_account.rs
@@ -36,8 +36,8 @@ use chrono;
 use hyper;
 use serde_json;
 
-const GRANT_TYPE: &'static str = "urn:ietf:params:oauth:grant-type:jwt-bearer";
-const GOOGLE_RS256_HEAD: &'static str = "{\"alg\":\"RS256\",\"typ\":\"JWT\"}";
+const GRANT_TYPE: &str = "urn:ietf:params:oauth:grant-type:jwt-bearer";
+const GOOGLE_RS256_HEAD: &str = "{\"alg\":\"RS256\",\"typ\":\"JWT\"}";
 
 /// Encodes s as Base64
 fn encode_base64<T: AsRef<[u8]>>(s: T) -> String {
@@ -51,7 +51,7 @@ fn decode_rsa_key(pem_pkcs8: &str) -> Result<PrivateKey, io::Error> {
     let private_keys = pemfile::pkcs8_private_keys(&mut private_reader);
 
     if let Ok(pk) = private_keys {
-        if pk.len() > 0 {
+        if !pk.is_empty() {
             Ok(pk[0].clone())
         } else {
             Err(io::Error::new(
@@ -112,7 +112,7 @@ impl JWT {
     fn new(claims: Claims) -> JWT {
         JWT {
             header: GOOGLE_RS256_HEAD.to_string(),
-            claims: claims,
+            claims,
         }
     }
 
@@ -141,10 +141,9 @@ impl JWT {
             .map_err(|_| io::Error::new(io::ErrorKind::Other, "Couldn't initialize signer"))?;
         let signer = signing_key
             .choose_scheme(&[rustls::SignatureScheme::RSA_PKCS1_SHA256])
-            .ok_or(io::Error::new(
-                io::ErrorKind::Other,
-                "Couldn't choose signing scheme",
-            ))?;
+            .ok_or_else(|| {
+                io::Error::new(io::ErrorKind::Other, "Couldn't choose signing scheme")
+            })?;
         let signature = signer
             .sign(jwt_head.as_bytes())
             .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, format!("{}", e)))?;
@@ -176,7 +175,7 @@ where
         iss: key.client_email.clone().unwrap(),
         aud: key.token_uri.clone().unwrap(),
         exp: expiry,
-        iat: iat,
+        iat,
         sub: None,
         scope: scopes_string,
     }
diff --git a/src/storage.rs b/src/storage.rs
index 8d9df5c..fef3c0a 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -103,17 +103,13 @@ impl TokenStorage for MemoryStorage {
             self.tokens.retain(|x| x.hash != scope_hash);
         }
 
-        match token {
-            Some(t) => {
-                tokens.push(JSONToken {
-                    hash: scope_hash,
-                    scopes: Some(scopes.into_iter().map(|x| x.as_ref().to_string()).collect()),
-                    token: t,
-                });
-                ()
-            }
-            None => {}
-        };
+        if let Some(t) = token {
+            tokens.push(JSONToken {
+                hash: scope_hash,
+                scopes: Some(scopes.iter().map(|x| x.as_ref().to_string()).collect()),
+                token: t,
+            });
+        }
         Ok(())
     }
 
@@ -233,10 +229,9 @@ impl TokenStorage for DiskTokenStorage {
                 Some(t) => {
                     tokens.push(JSONToken {
                         hash: scope_hash,
-                        scopes: Some(scopes.into_iter().map(|x| x.as_ref().to_string()).collect()),
+                        scopes: Some(scopes.iter().map(|x| x.as_ref().to_string()).collect()),
                         token: t,
                     });
-                    ()
                 }
             }
         }
diff --git a/src/types.rs b/src/types.rs
index 35ab2a4..a9d371c 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -91,7 +91,7 @@ impl From<JsonError> for RequestError {
             "invalid_scope" => RequestError::InvalidScope(
                 value
                     .error_description
-                    .unwrap_or("no description provided".to_string()),
+                    .unwrap_or_else(|| "no description provided".to_string()),
             ),
             _ => RequestError::NegativeServerResponse(value.error, value.error_description),
         }
@@ -112,7 +112,7 @@ impl fmt::Display for RequestError {
             RequestError::InvalidScope(ref scope) => writeln!(f, "Invalid Scope: '{}'", scope),
             RequestError::NegativeServerResponse(ref error, ref desc) => {
                 error.fmt(f)?;
-                if let &Some(ref desc) = desc {
+                if let Some(ref desc) = *desc {
                     write!(f, ": {}", desc)?;
                 }
                 "\n".fmt(f)
@@ -162,7 +162,7 @@ impl StringError {
             error.push_str(d.as_ref());
         }
 
-        StringError { error: error }
+        StringError { error }
     }
 }
 
@@ -298,7 +298,7 @@ impl Token {
     /// # Panics
     /// * if our access_token is unset
     pub fn expired(&self) -> bool {
-        if self.access_token.len() == 0 {
+        if self.access_token.is_empty() {
             panic!("called expired() on unset token");
         }
         if let Some(expiry_date) = self.expiry_date() {