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//! Module containing definitions and operations for type level booleans //! //! All operations are type aliases for convenience //! //! //! # Example //! //! Access of privileges based on renamed Boolean types. //! //! ``` //! use std::mem; //! use std::marker::PhantomData; //! use core_extensions::VariantPhantom; //! pub use core_extensions::type_level_bool::{ //! Boolean as PrivilegeLevel, //! False as Unprivileged , //! True as Privileged , //! }; //! //! //! //! #[derive(Debug)] //! struct User<P>{ //! name:String, //! privilege_level:VariantPhantom<P>, //! } //! //! impl<P:PrivilegeLevel> User<P>{ //! fn new(name:String,privilege_level:P)->Self{ //! Self{ name , privilege_level:PhantomData } //! } //! fn name(&self)->&str{ //! &self.name //! } //! fn into_unprivileged(self)->User<Unprivileged>{ //! User{ name:self.name , privilege_level:PhantomData } //! } //! fn as_unprivileged(self:&mut User<P>)->&mut User<Unprivileged>{ //! // Only the type parameter P changes here,which is itself a MarkerType. //! unsafe{ mem::transmute(self) } //! } //! } //! //! impl User<Privileged>{ //! fn set_name(&mut self,name:String){ //! self.name=name; //! } //! } //! //! let mut user:User<Privileged>= //! User::new("bob".into(),Privileged); //! assert_eq!(user.name(),"bob"); //! //! user.set_name("paul".into()); //! assert_eq!(user.name(),"paul"); //! //! { //! let user:&mut User<Unprivileged>= //! user.as_unprivileged(); //! //! // Unprivileged Users can't change their name. //! // user.set_name("james".into()); //! //! assert_eq!(user.name(),"paul"); //! } //! //! user.set_name("john".into()); //! assert_eq!(user.name(),"john"); //! //! ``` //! //! use VariantPhantom; use std_::fmt::Debug; use std_::ops; use marker_traits::MarkerType; /// Represents a type-level `true` #[derive(Debug, Copy, Clone, Default)] pub struct True; /// Represents a type-level `false` #[derive(Debug, Copy, Clone, Default)] pub struct False; /// Used to represent a type-level boolean when used as a type parameter. #[derive(Debug, Copy, Clone, Default)] pub struct BooleanType; mod sealed { use super::{False, True}; pub trait Sealed {} impl Sealed for True {} impl Sealed for False {} } use self::sealed::Sealed; unsafe impl MarkerType for True {} unsafe impl MarkerType for False {} /// Represents a type-level `bool` /// /// Only implemented on [True] and [False]. /// /// For examples look at [the module-level documentation](./index.html). /// /// This trait is sealed and cannot be implemented for types outside this crate. pub trait Boolean: Sealed + MarkerType + Default + Sized + Debug + Copy + Clone + ops::BitAnd<True> + ops::BitAnd<False> + ops::BitOr<True> + ops::BitOr<False> + ops::BitXor<True> + ops::BitXor<False> + ops::Not { /// The negation of this type. type Not: Boolean<Not = Self>; /// The [bool] value of this type const VALUE: bool; /// If Self==True,runs the closure and returns Some , otherwise returns None. fn if_true<U, F: FnOnce() -> U>(_: F) -> Option<U> { None } /// If Self==False,runs the closure and returns Some , otherwise returns None. fn if_false<U, F: FnOnce() -> U>(_: F) -> Option<U> { None } } impl Boolean for True { type Not = False; const VALUE: bool = true; fn if_true<U, F: FnOnce() -> U>(f: F) -> Option<U> { Some(f()) } } impl Boolean for False { type Not = True; const VALUE: bool = false; fn if_false<U, F: FnOnce() -> U>(f: F) -> Option<U> { Some(f()) } } /// pub mod internals { use super::*; /// Type that a Boolean operation evaluates to. pub trait BooleanOp { /// type Value; } #[doc(hidden)] /// Whether `B` is True or False.Usable for cases where either is required pub struct IsTrueOrFalse<B: Boolean>(VariantPhantom<B>); impl BooleanOp for IsTrueOrFalse<True> { type Value = True; } impl BooleanOp for IsTrueOrFalse<False> { type Value = True; } impl ops::Not for True { type Output = False; fn not(self) -> Self::Output { Default::default() } } impl ops::Not for False { type Output = True; fn not(self) -> Self::Output { Default::default() } } impl<B> ops::BitAnd<B> for False { type Output = False; fn bitand(self, _: B) -> Self::Output { Default::default() } } impl<B> ops::BitAnd<B> for True { type Output = B; fn bitand(self, v: B) -> Self::Output { v } } impl<B> ops::BitOr<B> for True { type Output = True; fn bitor(self, _: B) -> Self::Output { Default::default() } } impl<B> ops::BitOr<B> for False { type Output = B; fn bitor(self, v: B) -> Self::Output { v } } impl<B: Boolean> ops::BitXor<B> for True { type Output = B::Not; fn bitxor(self, _: B) -> Self::Output { Default::default() } } impl<B> ops::BitXor<B> for False { type Output = B; fn bitxor(self, v: B) -> Self::Output { v } } /// Struct representing a type-level if. pub struct IfElseOp<Cond, Then, Else>(VariantPhantom<(Cond, Then, Else)>); impl<Then, Else> BooleanOp for IfElseOp<True, Then, Else> { type Value = Then; } impl<Then, Else> BooleanOp for IfElseOp<False, Then, Else> { type Value = Else; } } pub use self::internals::*; /// Negates a [Boolean]. /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(Not::<True >::VALUE,false); /// /// assert_eq!(Not::<False>::VALUE,true); /// pub type Not<T> = <T as ops::Not>::Output; /// `And`s two [Boolean]s /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(And::<True ,True >::VALUE,true); /// /// assert_eq!(And::<False,True >::VALUE,false); /// /// assert_eq!(And::<True ,False>::VALUE,false); /// /// assert_eq!(And::<False,False>::VALUE,false); /// pub type And<L, R> = <L as ops::BitAnd<R>>::Output; /// `Or`s two [Boolean]s /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(Or::<True ,True >::VALUE,true); /// /// assert_eq!(Or::<False,True >::VALUE,true); /// /// assert_eq!(Or::<True ,False>::VALUE,true); /// /// assert_eq!(Or::<False,False>::VALUE,false); /// pub type Or<L, R> = <L as ops::BitOr<R>>::Output; /// `Nand`s two [Boolean]s /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(Nand::<True ,True >::VALUE,false); /// /// assert_eq!(Nand::<False,True >::VALUE,true); /// /// assert_eq!(Nand::<True ,False>::VALUE,true); /// /// assert_eq!(Nand::<False,False>::VALUE,true); /// pub type Nand<L, R> = Not<And<L, R>>; /// `Nor`s two [Boolean]s /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(Nor::<True ,True >::VALUE,false); /// /// assert_eq!(Nor::<False,True >::VALUE,false); /// /// assert_eq!(Nor::<True ,False>::VALUE,false); /// /// assert_eq!(Nor::<False,False>::VALUE,true); /// pub type Nor<L, R> = Not<Or<L, R>>; /// `Xor`s two [Boolean]s /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(Xor::<True ,True >::VALUE,false); /// /// assert_eq!(Xor::<False,True >::VALUE,true); /// /// assert_eq!(Xor::<True ,False>::VALUE,true); /// /// assert_eq!(Xor::<False,False>::VALUE,false); /// pub type Xor<L, R> = <L as ops::BitXor<R>>::Output; /// `Xnor`s two [Boolean]s /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(Xnor::<True ,True >::VALUE,true); /// /// assert_eq!(Xnor::<False,True >::VALUE,false); /// /// assert_eq!(Xnor::<True ,False>::VALUE,false); /// /// assert_eq!(Xnor::<False,False>::VALUE,true); /// pub type Xnor<L, R> = Not<Xor<L, R>>; /// Logical implication /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(Implies::<True ,True >::VALUE,true); /// /// assert_eq!(Implies::<False,True >::VALUE,true); /// /// assert_eq!(Implies::<True ,False>::VALUE,false); /// /// assert_eq!(Implies::<False,False>::VALUE,true); /// pub type Implies<L, R> = Or<Not<L>, R>; /// Material non-implication /// /// This type alias takes [Boolean] parameters and evaluates to /// either [True] or [False]. /// /// /// # use core_extensions::type_level_bool::*; /// assert_eq!(NonImp::<True ,True >::VALUE,false); /// /// assert_eq!(NonImp::<False,True >::VALUE,false); /// /// assert_eq!(NonImp::<True ,False>::VALUE,true ); /// /// assert_eq!(NonImp::<False,False>::VALUE,false); /// pub type NonImp<L, R> = And<L, Not<R>>; /// Type level conditional. /// /// if `Cond`==True the type is `Then`. /// /// if `Cond`==False the type is `Else`. /// /// This will be more ergonomic once specialization is stable. /// /// # Example /// /// ``` /// use core_extensions::type_level_bool::{IfElse,True,False}; /// let a:IfElse<True ,i32,&str>=0; /// let b:IfElse<False,i32,&str>="type level conditionals"; /// ``` /// /// # Example of field whose type depends on a [Boolean](::type_level_bool::Boolean). /// /// Currently it is necessary to add a where clause to the type containing a conditional field, /// this limitation will be lifted once specialization is stable. /// /// ``` /// use core_extensions::VariantPhantom; /// use core_extensions::type_level_bool::{IfElse,Boolean,False,True}; /// use core_extensions::type_level_bool::internals::{IfElseOp,BooleanOp}; /// /// struct Conditional<ZST> /// where /// IfElseOp<ZST,&'static str,usize>:BooleanOp, /// { /// pub value:IfElse<ZST,&'static str,usize>, /// pub cond:ZST, /// } /// /// let string_=Conditional{ value:"wtf" ,cond:True }; /// let int_ =Conditional{ value:99 ,cond:False }; /// /// // The 2 lines bellow won't compile. /// // let string_=Conditional{ value:"wtf",cond:False }; /// // let int_ =Conditional{ value:99 ,cond:True }; /// ``` /// /// /// /// pub type IfElse<Cond, Then, Else> = <IfElseOp<Cond, Then, Else> as BooleanOp>::Value;