avoid allocating string

ethcore/src/builtin.rs

@@ -28,11 +28,11 @@ use ethkey::{Signature, recover as ec_recover};
 use ethjson;
 
 #[derive(Debug)]
-pub struct Error(pub String);
+pub struct Error(pub &'static str);
 
 impl From<&'static str> for Error {
 	fn from(val: &'static str) -> Self {
-		Error(val.to_owned())
+		Error(val)
 	}
 }
 

ethcore/src/evm/evm.rs

@@ -61,7 +61,7 @@ pub enum Error {
 		limit: usize
 	},
 	/// Built-in contract failed on given input
-	BuiltIn(String),
+	BuiltIn(&'static str),
 	/// Returned on evm internal error. Should never be ignored during development.
 	/// Likely to cause consensus issues.
 	Internal(String),