Merge pull request #6461 from paritytech/util_error_chain

UtilError utilizes error_chain!

Cargo.lock

@@ -455,6 +455,14 @@ dependencies = [
  "backtrace 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "error-chain"
+version = "0.11.0-rc.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "backtrace 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "eth-secp256k1"
 version = "0.5.6"
@@ -547,6 +555,7 @@ dependencies = [
  "time 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "transient-hashmap 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "triehash 0.1.0",
+ "unexpected 0.1.0",
  "using_queue 0.1.0",
  "vm 0.1.0",
  "wasm 0.1.0",
@@ -796,6 +805,7 @@ dependencies = [
  "clippy 0.0.103 (registry+https://github.com/rust-lang/crates.io-index)",
  "elastic-array 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "env_logger 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "error-chain 0.11.0-rc.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "eth-secp256k1 0.5.6 (git+https://github.com/paritytech/rust-secp256k1)",
  "ethcore-bigint 0.1.3",
  "ethcore-bloom-journal 0.1.0",
@@ -3144,6 +3154,10 @@ name = "typeable"
 version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "unexpected"
+version = "0.1.0"
+
 [[package]]
 name = "unicase"
 version = "1.4.0"
@@ -3395,6 +3409,7 @@ dependencies = [
 "checksum either 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "3d2b503c86dad62aaf414ecf2b8c527439abedb3f8d812537f0b12bfd6f32a91"
 "checksum elastic-array 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "258ff6a9a94f648d0379dbd79110e057edbb53eb85cc237e33eadf8e5a30df85"
 "checksum env_logger 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e3856f1697098606fc6cb97a93de88ca3f3bc35bb878c725920e6e82ecf05e83"
+"checksum error-chain 0.11.0-rc.2 (registry+https://github.com/rust-lang/crates.io-index)" = "38d3a55d9a7a456748f2a3912c0941a5d9a68006eb15b3c3c9836b8420dc102d"
 "checksum error-chain 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "bd5c82c815138e278b8dcdeffc49f27ea6ffb528403e9dea4194f2e3dd40b143"
 "checksum eth-secp256k1 0.5.6 (git+https://github.com/paritytech/rust-secp256k1)" = "<none>"
 "checksum ethabi 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0c3d62319ee0f35abf20afe8859dd2668195912614346447bb2dee9fb8da7c62"

ethcore/Cargo.toml

@@ -66,6 +66,7 @@ wasm = { path = "wasm" }
 hash = { path = "../util/hash" }
 triehash = { path = "../util/triehash" }
 semantic_version = { path = "../util/semantic_version" }
+unexpected = { path = "../util/unexpected" }
 
 [dev-dependencies]
 native-contracts = { path = "native_contracts", features = ["test_contracts"] }

ethcore/src/block.rs

@@ -26,7 +26,7 @@ use rlp::{UntrustedRlp, RlpStream, Encodable, Decodable, DecoderError};
 use bigint::prelude::U256;
 use bigint::hash::H256;
 use util::{Bytes, Address};
-use util::error::{Mismatch, OutOfBounds};
+use unexpected::{Mismatch, OutOfBounds};
 
 use basic_types::{LogBloom, Seal};
 use vm::{EnvInfo, LastHashes};

ethcore/src/client/client.rs

@@ -25,6 +25,7 @@ use itertools::Itertools;
 // util
 use hash::keccak;
 use timer::PerfTimer;
+use util::UtilError;
 use util::Bytes;
 use util::{journaldb, DBValue, TrieFactory, Trie};
 use util::Address;
@@ -252,7 +253,7 @@ impl Client {
 			last_hashes: RwLock::new(VecDeque::new()),
 			factories: factories,
 			history: history,
-			rng: Mutex::new(OsRng::new().map_err(::util::UtilError::StdIo)?),
+			rng: Mutex::new(OsRng::new().map_err(UtilError::from)?),
 			ancient_verifier: Mutex::new(None),
 			on_user_defaults_change: Mutex::new(None),
 			registrar: Mutex::new(None),

ethcore/src/engines/authority_round/mod.rs

@@ -46,6 +46,7 @@ use bigint::prelude::{U256, U128};
 use bigint::hash::{H256, H520};
 use semantic_version::SemanticVersion;
 use parking_lot::{Mutex, RwLock};
+use unexpected::{Mismatch, OutOfBounds};
 use util::*;
 
 mod finality;

ethcore/src/engines/basic_authority.rs

@@ -23,6 +23,7 @@ use bigint::prelude::U256;
 use bigint::hash::{H256, H520};
 use parking_lot::RwLock;
 use util::*;
+use unexpected::{Mismatch, OutOfBounds};
 use ethkey::{recover, public_to_address, Signature};
 use account_provider::AccountProvider;
 use block::*;

ethcore/src/engines/mod.rs

@@ -58,6 +58,7 @@ use bigint::prelude::U256;
 use bigint::hash::H256;
 use semantic_version::SemanticVersion;
 use util::*;
+use unexpected::{Mismatch, OutOfBounds};
 
 /// Default EIP-210 contrat code.
 /// As defined in https://github.com/ethereum/EIPs/pull/210/commits/9df24a3714af42e3bf350265bdc75b486c909d7f#diff-e02a92c2fb96c1a1bfb05e4c6e2ef5daR49

ethcore/src/engines/tendermint/mod.rs

@@ -34,6 +34,7 @@ use bigint::prelude::{U128, U256};
 use bigint::hash::{H256, H520};
 use parking_lot::RwLock;
 use util::*;
+use unexpected::{OutOfBounds, Mismatch};
 use client::{Client, EngineClient};
 use error::{Error, BlockError};
 use header::{Header, BlockNumber};

ethcore/src/engines/validator_set/safe_contract.rs

@@ -26,6 +26,7 @@ use bigint::hash::{H160, H256};
 use parking_lot::RwLock;
 use util::*;
 use util::cache::MemoryLruCache;
+use unexpected::Mismatch;
 use rlp::{UntrustedRlp, RlpStream};
 
 use basic_types::LogBloom;

ethcore/src/error.rs

@@ -20,6 +20,7 @@ use std::fmt;
 use bigint::prelude::U256;
 use bigint::hash::H256;
 use util::*;
+use unexpected::{Mismatch, OutOfBounds};
 use io::*;
 use header::BlockNumber;
 use basic_types::LogBloom;
@@ -394,7 +395,7 @@ impl From<ExecutionError> for Error {
 
 impl From<::rlp::DecoderError> for Error {
 	fn from(err: ::rlp::DecoderError) -> Error {
-		Error::Util(UtilError::Decoder(err))
+		Error::Util(UtilError::from(err))
 	}
 }
 
@@ -427,7 +428,7 @@ impl From<BlockImportError> for Error {
 		match err {
 			BlockImportError::Block(e) => Error::Block(e),
 			BlockImportError::Import(e) => Error::Import(e),
-			BlockImportError::Other(s) => Error::Util(UtilError::SimpleString(s)),
+			BlockImportError::Other(s) => Error::Util(UtilError::from(s)),
 		}
 	}
 }

ethcore/src/ethereum/ethash.rs

@@ -23,6 +23,7 @@ use ethash::{quick_get_difficulty, slow_get_seedhash, EthashManager};
 use bigint::prelude::U256;
 use bigint::hash::{H256, H64};
 use util::*;
+use unexpected::{OutOfBounds, Mismatch};
 use block::*;
 use builtin::Builtin;
 use vm::EnvInfo;

ethcore/src/lib.rs

@@ -108,6 +108,7 @@ extern crate heapsize;
 extern crate triehash;
 extern crate ansi_term;
 extern crate semantic_version;
+extern crate unexpected;
 
 #[macro_use]
 extern crate rlp_derive;

ethcore/src/snapshot/service.rs

@@ -102,7 +102,7 @@ impl Restoration {
 		let block_chunks = manifest.block_hashes.iter().cloned().collect();
 
 		let raw_db = Arc::new(Database::open(params.db_config, &*params.db_path.to_string_lossy())
-			.map_err(UtilError::SimpleString)?);
+			.map_err(UtilError::from)?);
 
 		let chain = BlockChain::new(Default::default(), params.genesis, raw_db.clone());
 		let components = params.engine.snapshot_components()
@@ -519,7 +519,7 @@ impl Service {
 
 							match is_done {
 								true => {
-									db.flush().map_err(::util::UtilError::SimpleString)?;
+									db.flush().map_err(UtilError::from)?;
 									drop(db);
 									return self.finalize_restoration(&mut *restoration);
 								},
@@ -532,7 +532,7 @@ impl Service {
 				}
 			}
 		};
-		result.and_then(|_| db.flush().map_err(|e| ::util::UtilError::SimpleString(e).into()))
+		result.and_then(|_| db.flush().map_err(|e| UtilError::from(e).into()))
 	}
 
 	/// Feed a state chunk to be processed synchronously.

ethcore/src/transaction.rs

@@ -380,7 +380,7 @@ impl UnverifiedTransaction {
 			self.recover_public()?;
 		}
 		if self.gas < U256::from(self.gas_required(&schedule)) {
-			return Err(TransactionError::InvalidGasLimit(::util::OutOfBounds{min: Some(U256::from(self.gas_required(&schedule))), max: None, found: self.gas}).into())
+			return Err(TransactionError::InvalidGasLimit(::unexpected::OutOfBounds{min: Some(U256::from(self.gas_required(&schedule))), max: None, found: self.gas}).into())
 		}
 		Ok(self)
 	}

ethcore/src/verification/verification.rs

@@ -27,6 +27,7 @@ use triehash::ordered_trie_root;
 use heapsize::HeapSizeOf;
 use bigint::hash::H256;
 use util::*;
+use unexpected::{Mismatch, OutOfBounds};
 use engines::Engine;
 use error::{BlockError, Error};
 use blockchain::*;
@@ -274,6 +275,7 @@ mod tests {
 	use bigint::prelude::U256;
 	use bigint::hash::{H256, H2048};
 	use triehash::ordered_trie_root;
+	use unexpected::{Mismatch, OutOfBounds};
 	use util::*;
 	use ethkey::{Random, Generator};
 	use header::*;

util/Cargo.toml

@@ -34,6 +34,7 @@ regex = "0.2"
 lru-cache = "0.1.0"
 ethcore-logger = { path = "../logger" }
 triehash = { path = "triehash" }
+error-chain = "0.11.0-rc.2"
 
 [features]
 default = []

util/network/src/error.rs

@@ -16,7 +16,6 @@
 
 use io::IoError;
 use rlp::*;
-use util::UtilError;
 use std::fmt;
 use ethkey::Error as KeyError;
 use crypto::Error as CryptoError;
@@ -96,8 +95,8 @@ pub enum NetworkError {
 	PeerNotFound,
 	/// Peer is diconnected.
 	Disconnect(DisconnectReason),
-	/// Util error.
+	/// Invalid NodeId
-	Util(UtilError),
+	InvalidNodeId,
 	/// Socket IO error.
 	Io(IoError),
 	/// Error concerning the network address parsing subsystem.
@@ -125,7 +124,7 @@ impl fmt::Display for NetworkError {
 			AddressResolve(Some(ref err)) => format!("{}", err),
 			AddressResolve(_) => "Failed to resolve network address.".into(),
 			StdIo(ref err) => format!("{}", err),
-			Util(ref err) => format!("{}", err),
+			InvalidNodeId => "Invalid node id".into(),
 			OversizedPacket => "Packet is too large".into(),
 		};
 
@@ -151,12 +150,6 @@ impl From<IoError> for NetworkError {
 	}
 }
 
-impl From<UtilError> for NetworkError {
-	fn from(err: UtilError) -> NetworkError {
-		NetworkError::Util(err)
-	}
-}
-
 impl From<KeyError> for NetworkError {
 	fn from(_err: KeyError) -> Self {
 		NetworkError::Auth

util/network/src/node_table.rs

@@ -26,7 +26,6 @@ use std::fmt;
 use std::fs;
 use std::io::{Read, Write};
 use bigint::hash::*;
-use util::UtilError;
 use rlp::*;
 use time::Tm;
 use error::NetworkError;
@@ -175,7 +174,7 @@ impl FromStr for Node {
 	type Err = NetworkError;
 	fn from_str(s: &str) -> Result<Self, Self::Err> {
 		let (id, endpoint) = if s.len() > 136 && &s[0..8] == "enode://" && &s[136..137] == "@" {
-			(s[8..136].parse().map_err(UtilError::from)?, NodeEndpoint::from_str(&s[137..])?)
+			(s[8..136].parse().map_err(|_| NetworkError::InvalidNodeId)?, NodeEndpoint::from_str(&s[137..])?)
 		}
 		else {
 			(NodeId::new(), NodeEndpoint::from_str(s)?)

util/src/error.rs

@@ -16,9 +16,12 @@
 
 //! General error types for use in ethcore.
 
+#![allow(missing_docs)]
+#![allow(unknown_lints)]
+
+use std::{self, fmt};
 use rustc_hex::FromHexError;
 use rlp::DecoderError;
-use std::fmt;
 use bigint::hash::H256;
 
 #[derive(Debug)]
@@ -41,124 +44,23 @@ impl fmt::Display for BaseDataError {
 	}
 }
 
-#[derive(Debug)]
+impl std::error::Error for BaseDataError {
-/// General error type which should be capable of representing all errors in ethcore.
+	fn description(&self) -> &str {
-pub enum UtilError {
+		"Error in database subsystem"
-	/// Error concerning the Rust standard library's IO subsystem.
-	StdIo(::std::io::Error),
-	/// Error concerning the hex conversion logic.
-	FromHex(FromHexError),
-	/// Error concerning the database abstraction logic.
-	BaseData(BaseDataError),
-	/// Error concerning the RLP decoder.
-	Decoder(DecoderError),
-	/// Miscellaneous error described by a string.
-	SimpleString(String),
-	/// Error from a bad input size being given for the needed output.
-	BadSize,
-	/// Error from snappy.
-	Snappy(::snappy::InvalidInput),
-}
-
-impl fmt::Display for UtilError {
-	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-		match *self {
-			UtilError::StdIo(ref err) => f.write_fmt(format_args!("{}", err)),
-			UtilError::FromHex(ref err) => f.write_fmt(format_args!("{}", err)),
-			UtilError::BaseData(ref err) => f.write_fmt(format_args!("{}", err)),
-			UtilError::Decoder(ref err) => f.write_fmt(format_args!("{}", err)),
-			UtilError::SimpleString(ref msg) => f.write_str(msg),
-			UtilError::BadSize => f.write_str("Bad input size."),
-			UtilError::Snappy(ref err) => f.write_fmt(format_args!("{}", err)),
-		}
 	}
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+error_chain! {
-/// Error indicating an expected value was not found.
+	types {
-pub struct Mismatch<T: fmt::Debug> {
+		UtilError, ErrorKind, ResultExt, Result;
-	/// Value expected.
+	}
-	pub expected: T,
-	/// Value found.
-	pub found: T,
-}
 
-impl<T: fmt::Debug + fmt::Display> fmt::Display for Mismatch<T> {
+	foreign_links {
-	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		Io(::std::io::Error);
-		f.write_fmt(format_args!("Expected {}, found {}", self.expected, self.found))
+		FromHex(FromHexError);
+		Decoder(DecoderError);
+		Snappy(::snappy::InvalidInput);
+		BaseData(BaseDataError);
 	}
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
-/// Error indicating value found is outside of a valid range.
-pub struct OutOfBounds<T: fmt::Debug> {
-	/// Minimum allowed value.
-	pub min: Option<T>,
-	/// Maximum allowed value.
-	pub max: Option<T>,
-	/// Value found.
-	pub found: T,
-}
-
-impl<T: fmt::Debug + fmt::Display> fmt::Display for OutOfBounds<T> {
-	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-		let msg = match (self.min.as_ref(), self.max.as_ref()) {
-			(Some(min), Some(max)) => format!("Min={}, Max={}", min, max),
-			(Some(min), _) => format!("Min={}", min),
-			(_, Some(max)) => format!("Max={}", max),
-			(None, None) => "".into(),
-		};
-
-		f.write_fmt(format_args!("Value {} out of bounds. {}", self.found, msg))
-	}
-}
-
-impl From<FromHexError> for UtilError {
-	fn from(err: FromHexError) -> UtilError {
-		UtilError::FromHex(err)
-	}
-}
-
-impl From<BaseDataError> for UtilError {
-	fn from(err: BaseDataError) -> UtilError {
-		UtilError::BaseData(err)
-	}
-}
-
-impl From<::std::io::Error> for UtilError {
-	fn from(err: ::std::io::Error) -> UtilError {
-		UtilError::StdIo(err)
-	}
-}
-
-impl From<::rlp::DecoderError> for UtilError {
-	fn from(err: ::rlp::DecoderError) -> UtilError {
-		UtilError::Decoder(err)
-	}
-}
-
-impl From<String> for UtilError {
-	fn from(err: String) -> UtilError {
-		UtilError::SimpleString(err)
-	}
-}
-
-impl From<::snappy::InvalidInput> for UtilError {
-	fn from(err: ::snappy::InvalidInput) -> UtilError {
-		UtilError::Snappy(err)
-	}
-}
-
-// TODO: uncomment below once https://github.com/rust-lang/rust/issues/27336 sorted.
-/*#![feature(concat_idents)]
-macro_rules! assimilate {
-    ($name:ident) => (
-		impl From<concat_idents!($name, Error)> for Error {
-			fn from(err: concat_idents!($name, Error)) -> Error {
-				Error:: $name (err)
-			}
-		}
-    )
-}
-assimilate!(FromHex);
-assimilate!(BaseData);*/

util/src/journaldb/archivedb.rs

@@ -26,7 +26,8 @@ use super::{DB_PREFIX_LEN, LATEST_ERA_KEY};
 use super::traits::JournalDB;
 use kvdb::{KeyValueDB, DBTransaction};
 use bigint::hash::H256;
-use {Bytes, BaseDataError, UtilError};
+use error::{BaseDataError, UtilError};
+use {Bytes};
 
 /// Implementation of the `HashDB` trait for a disk-backed database with a memory overlay
 /// and latent-removal semantics.

util/src/journaldb/earlymergedb.rs

@@ -29,7 +29,8 @@ use super::{DB_PREFIX_LEN, LATEST_ERA_KEY};
 use super::traits::JournalDB;
 use kvdb::{KeyValueDB, DBTransaction};
 use bigint::hash::H256;
-use { BaseDataError, UtilError, Bytes};
+use error::{BaseDataError, UtilError};
+use {Bytes};
 
 #[derive(Clone, PartialEq, Eq)]
 struct RefInfo {

util/src/journaldb/overlayrecentdb.rs

@@ -28,7 +28,8 @@ use super::{DB_PREFIX_LEN, LATEST_ERA_KEY};
 use kvdb::{KeyValueDB, DBTransaction};
 use super::JournalDB;
 use bigint::hash::{H256, H256FastMap};
-use {BaseDataError, UtilError, Bytes};
+use error::{BaseDataError, UtilError};
+use {Bytes};
 
 /// Implementation of the `JournalDB` trait for a disk-backed database with a memory overlay
 /// and, possibly, latent-removal semantics.

util/src/kvdb.rs

@@ -279,7 +279,7 @@ impl KeyValueDB for InMemory {
 	}
 
 	fn restore(&self, _new_db: &str) -> Result<(), UtilError> {
-		Err(UtilError::SimpleString("Attempted to restore in-memory database".into()))
+		Err("Attempted to restore in-memory database".into())
 	}
 }
 

util/src/lib.rs

@@ -109,6 +109,9 @@ extern crate heapsize;
 extern crate ethcore_logger;
 extern crate hash as keccak;
 
+#[macro_use]
+extern crate error_chain;
+
 #[macro_use]
 extern crate log as rlog;
 
@@ -136,7 +139,7 @@ pub use overlaydb::*;
 pub use journaldb::JournalDB;
 pub use trie::{Trie, TrieMut, TrieDB, TrieDBMut, TrieFactory, TrieError, SecTrieDB, SecTrieDBMut};
 pub use kvdb::*;
-pub use error::*;
+pub use error::UtilError;
 pub use bytes::*;
 
 /// 160-bit integer representing account address

util/src/overlaydb.rs

@@ -19,7 +19,7 @@
 use std::sync::Arc;
 use std::collections::HashMap;
 use std::collections::hash_map::Entry;
-use error::*;
+use error::{Result, BaseDataError};
 use bigint::hash::*;
 use rlp::*;
 use hashdb::*;
@@ -56,14 +56,14 @@ impl OverlayDB {
 
 	/// Commit all operations in a single batch.
 	#[cfg(test)]
-	pub fn commit(&mut self) -> Result<u32, UtilError> {
+	pub fn commit(&mut self) -> Result<u32> {
 		let mut batch = self.backing.transaction();
 		let res = self.commit_to_batch(&mut batch)?;
 		self.backing.write(batch).map(|_| res).map_err(|e| e.into())
 	}
 
 	/// Commit all operations to given batch.
-	pub fn commit_to_batch(&mut self, batch: &mut DBTransaction) -> Result<u32, UtilError> {
+	pub fn commit_to_batch(&mut self, batch: &mut DBTransaction) -> Result<u32> {
 		let mut ret = 0u32;
 		let mut deletes = 0usize;
 		for i in self.overlay.drain() {

util/src/snappy.rs

@@ -16,7 +16,7 @@
 
 //! Snappy compression bindings.
 
-use std::fmt;
+use std::{self, fmt};
 use libc::{c_char, c_int, size_t};
 
 const SNAPPY_OK: c_int = 0;
@@ -56,6 +56,12 @@ extern {
 #[derive(Debug)]
 pub struct InvalidInput;
 
+impl std::error::Error for InvalidInput {
+	fn description(&self) -> &str {
+		"Attempted snappy decompression with invalid input"
+	}
+}
+
 impl fmt::Display for InvalidInput {
 	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 		write!(f, "Attempted snappy decompression with invalid input")

util/unexpected/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "unexpected"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+
+[dependencies]

util/unexpected/src/lib.rs

@@ -0,0 +1,58 @@
+// Copyright 2015-2017 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Error utils
+
+use std::fmt;
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+/// Error indicating an expected value was not found.
+pub struct Mismatch<T> {
+	/// Value expected.
+	pub expected: T,
+	/// Value found.
+	pub found: T,
+}
+
+impl<T: fmt::Display> fmt::Display for Mismatch<T> {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		f.write_fmt(format_args!("Expected {}, found {}", self.expected, self.found))
+	}
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+/// Error indicating value found is outside of a valid range.
+pub struct OutOfBounds<T> {
+	/// Minimum allowed value.
+	pub min: Option<T>,
+	/// Maximum allowed value.
+	pub max: Option<T>,
+	/// Value found.
+	pub found: T,
+}
+
+impl<T: fmt::Display> fmt::Display for OutOfBounds<T> {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		let msg = match (self.min.as_ref(), self.max.as_ref()) {
+			(Some(min), Some(max)) => format!("Min={}, Max={}", min, max),
+			(Some(min), _) => format!("Min={}", min),
+			(_, Some(max)) => format!("Max={}", max),
+			(None, None) => "".into(),
+		};
+
+		f.write_fmt(format_args!("Value {} out of bounds. {}", self.found, msg))
+	}
+}