lib.rs

// This file is part of Substrate.

// Copyright (C) 2017-2020 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Support code for the runtime.

#![cfg_attr(not(feature = "std"), no_std)]

/// Export ourself as `frame_support` to make tests happy.
extern crate self as frame_support;

#[doc(hidden)]
pub use sp_tracing;

#[cfg(feature = "std")]
pub use serde;
pub use sp_core::Void;
#[doc(hidden)]
pub use sp_std;
#[doc(hidden)]
pub use codec;
#[cfg(feature = "std")]
#[doc(hidden)]
pub use once_cell;
#[doc(hidden)]
pub use paste;
#[cfg(feature = "std")]
#[doc(hidden)]
pub use sp_state_machine::BasicExternalities;
#[doc(hidden)]
pub use sp_io::{storage::root as storage_root, self};
#[doc(hidden)]
pub use sp_runtime::RuntimeDebug;

#[macro_use]
pub mod debug;
#[macro_use]
mod origin;
#[macro_use]
pub mod dispatch;
pub mod storage;
mod hash;
#[macro_use]
pub mod event;
#[macro_use]
pub mod metadata;
#[macro_use]
pub mod genesis_config;
#[macro_use]
pub mod inherent;
#[macro_use]
pub mod unsigned;
#[macro_use]
pub mod error;
pub mod traits;
pub mod weights;

pub use self::hash::{
	Twox256, Twox128, Blake2_256, Blake2_128, Identity, Twox64Concat, Blake2_128Concat, Hashable,
	StorageHasher, ReversibleStorageHasher
};
pub use self::storage::{
	StorageValue, StorageMap, StorageDoubleMap, StoragePrefixedMap, IterableStorageMap,
	IterableStorageDoubleMap, migration
};
pub use self::dispatch::{Parameter, Callable};
pub use sp_runtime::{self, ConsensusEngineId, print, traits::Printable};

/// A type that cannot be instantiated.
#[derive(Debug)]
pub enum Never {}

/// Create new implementations of the [`Get`](crate::traits::Get) trait.
///
/// The so-called parameter type can be created in four different ways:
///
/// - Using `const` to create a parameter type that provides a `const` getter. It is required that
///   the `value` is const.
///
/// - Declare the parameter type without `const` to have more freedom when creating the value.
///
/// - Using `storage` to create a storage parameter type. This type is special as it tries to load
///   the value from the storage under a fixed key. If the value could not be found in the storage,
///   the given default value will be returned. It is required that the value implements
///   [`Encode`](codec::Encode) and [`Decode`](codec::Decode). The key for looking up the value in
///   the storage is built using the following formula:
///
///   `twox_128(":" ++ NAME ++ ":")` where `NAME` is the name that is passed as type name.
///
/// - Using `static` to create a static parameter type. Its value is
///   being provided by a static variable with the equivalent name in `UPPER_SNAKE_CASE`. An
///   additional `set` function is provided in this case to alter the static variable. 
///
/// **This is intended for testing ONLY and is ONLY available when `std` is enabled**
///
/// # Examples
///
/// ```
/// # use frame_support::traits::Get;
/// # use frame_support::parameter_types;
/// // This function cannot be used in a const context.
/// fn non_const_expression() -> u64 { 99 }
///
/// const FIXED_VALUE: u64 = 10;
/// parameter_types! {
///    pub const Argument: u64 = 42 + FIXED_VALUE;
///    /// Visibility of the type is optional
///    OtherArgument: u64 = non_const_expression();
///    pub storage StorageArgument: u64 = 5;
///    pub static StaticArgument: u32 = 7;
/// }
///
/// trait Config {
///    type Parameter: Get<u64>;
///    type OtherParameter: Get<u64>;
///    type StorageParameter: Get<u64>;
///    type StaticParameter: Get<u32>;
/// }
///
/// struct Runtime;
/// impl Config for Runtime {
///    type Parameter = Argument;
///    type OtherParameter = OtherArgument;
///    type StorageParameter = StorageArgument;
///    type StaticParameter = StaticArgument;
/// }
///
/// // In testing, `StaticArgument` can be altered later: `StaticArgument::set(8)`.
/// ```
///
/// # Invalid example:
///
/// ```compile_fail
/// # use frame_support::traits::Get;
/// # use frame_support::parameter_types;
/// // This function cannot be used in a const context.
/// fn non_const_expression() -> u64 { 99 }
///
/// parameter_types! {
///    pub const Argument: u64 = non_const_expression();
/// }
/// ```
#[macro_export]
macro_rules! parameter_types {
	(
		$( #[ $attr:meta ] )*
		$vis:vis const $name:ident: $type:ty = $value:expr;
		$( $rest:tt )*
	) => (
		$( #[ $attr ] )*
		$vis struct $name;
		$crate::parameter_types!(IMPL_CONST $name , $type , $value);
		$crate::parameter_types!( $( $rest )* );
	);
	(
		$( #[ $attr:meta ] )*
		$vis:vis $name:ident: $type:ty = $value:expr;
		$( $rest:tt )*
	) => (
		$( #[ $attr ] )*
		$vis struct $name;
		$crate::parameter_types!(IMPL $name, $type, $value);
		$crate::parameter_types!( $( $rest )* );
	);
	(
		$( #[ $attr:meta ] )*
		$vis:vis storage $name:ident: $type:ty = $value:expr;
		$( $rest:tt )*
	) => (
		$( #[ $attr ] )*
		$vis struct $name;
		$crate::parameter_types!(IMPL_STORAGE $name, $type, $value);
		$crate::parameter_types!( $( $rest )* );
	);
	() => ();
	(IMPL_CONST $name:ident, $type:ty, $value:expr) => {
		impl $name {
			/// Returns the value of this parameter type.
			pub const fn get() -> $type {
				$value
			}
		}

		impl<I: From<$type>> $crate::traits::Get<I> for $name {
			fn get() -> I {
				I::from($value)
			}