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use std_::mem; #[cfg(feature = "std")] use std::rc::Rc; #[cfg(feature = "std")] use std::sync::Arc; use utils::transmute_ignore_size; /// Allows converting `Self` to /// [`Self::Type`](./trait.Identity.html#associatedtype.Type) /// by proving that both types are equal. /// /// For extension methods of types, /// either generic (`Vec<T>`) or fully concrete (`str`), /// to avoid repeating method and function signatures in both the trait and the impl block. /// /// To create a type Alias in a where clause ,eg:` Vec<i32>:TypeIdentity<Type=List> `. /// /// To unwrap a generic type ,eg:` I:TypeIdentity<Type=Option<U>> `. /// /// # Example /// Defining an extension trait on Vec<T>. /// /// ``` /// use core_extensions::TypeIdentity; /// /// trait VecExt<T>:TypeIdentity<Type=Vec<T>>{ /// fn is_nonempty(&self)->bool{ /// !self.into_type_ref().is_empty() /// } /// fn moved_vec(self)->Vec<T> /// where Self:Sized /// { /// self.into_type_val() /// } /// fn mutable_vec(&mut self)->&mut Vec<T>{ /// self.into_type_mut() /// } /// } /// impl<T> VecExt<T> for Vec<T> {} /// /// assert!( vec![100].is_nonempty() ); /// assert!( !Vec::<i32>::new().is_nonempty() ); /// ``` /// /// /// /// /// # Example of a method requiring Self==Other /// Wrapper::iter is only callable on Wrapper\<Vec\<T>> /// /// ``` /// use core_extensions::TypeIdentity; /// use std::slice; /// /// struct Wrapper<U>(U); /// /// impl<U> Wrapper<U>{ /// fn iter<T>(&self)->slice::Iter<T> /// where U:TypeIdentity<Type=Vec<T>> /// { /// self.0.into_type_ref().iter() /// } /// } /// /// assert_eq!( /// Wrapper(vec![0,1,2,3,4]).iter().cloned().collect::<Vec<_>>() , /// vec![0,1,2,3,4] /// ); /// /// ``` /// /// /// # Example of creating a type alias in a where clause /// /// ``` /// use core_extensions::TypeIdentity; /// use std::ops::Deref; /// /// struct Example<T>(T); /// /// impl<T,Target0,Target1> Deref for Example<T> /// where /// T:Deref, /// <T as Deref>::Target:TypeIdentity<Type=Target0>, /// Target0:Deref, /// <Target0 as Deref>::Target:TypeIdentity<Type=Target1>, /// { /// type Target=Target1; /// /// fn deref(&self)->&Target1{ /// &**self /// } /// } /// /// ``` /// /// pub trait TypeIdentity { /// The same type as Self. /// /// Used in bounds to require that a generic type is a particular type. type Type: ?Sized; /// Converts a value back to the original type. #[inline(always)] fn into_type_val(self) -> Self::Type where Self: Sized, Self::Type: Sized, { unsafe { transmute_ignore_size(self) } } /// Converts a reference back to the original type. #[inline(always)] fn into_type_ref(&self) -> &Self::Type { unsafe { mem::transmute_copy::<&Self, &Self::Type>(&self) } } /// Converts a mutable reference back to the original type. #[inline(always)] fn into_type_mut(&mut self) -> &mut Self::Type { unsafe { mem::transmute_copy::<&mut Self, &mut Self::Type>(&self) } } /// Converts a box back to the original type. #[cfg(feature = "std")] #[inline(always)] fn into_type_box(self: Box<Self>) -> Box<Self::Type> { unsafe { transmute_ignore_size(self) } } /// Converts an Arc back to the original type. #[cfg(feature = "std")] #[inline(always)] fn into_type_arc(this: Arc<Self>) -> Arc<Self::Type> { unsafe { transmute_ignore_size(this) } } /// Converts an Rc back to the original type. #[cfg(feature = "std")] #[inline(always)] fn into_type_rc(this: Rc<Self>) -> Rc<Self::Type> { unsafe { transmute_ignore_size(this) } } /// Converts a value back to the original type. #[inline(always)] fn from_type_val(this: Self::Type) -> Self where Self: Sized, Self::Type: Sized, { let this = mem::ManuallyDrop::new(this); unsafe { mem::transmute_copy::<Self::Type, Self>(&*this) } } /// Converts a reference back to the original type. #[inline(always)] fn from_type_ref(this: &Self::Type) -> &Self { unsafe { mem::transmute_copy::<&Self::Type, &Self>(&this) } } /// Converts a mutable reference back to the original type. #[inline(always)] fn from_type_mut(this: &mut Self::Type) -> &mut Self { unsafe { mem::transmute_copy::<&mut Self::Type, &mut Self>(&this) } } /// Converts a box back to the original type. #[cfg(feature = "std")] #[inline(always)] fn from_type_box(this: Box<Self::Type>) -> Box<Self> { unsafe { transmute_ignore_size(this) } } /// Converts an Arc back to the original type. #[cfg(feature = "std")] #[inline(always)] fn from_type_arc(this: Arc<Self::Type>) -> Arc<Self> { unsafe { transmute_ignore_size(this) } } /// Converts an Rc back to the original type. #[cfg(feature = "std")] #[inline(always)] fn from_type_rc(this: Rc<Self::Type>) -> Rc<Self> { unsafe { transmute_ignore_size(this) } } #[doc(hidden)] #[allow(dead_code)] /// Prevents creating a trait object of this trait fn _dummy_generic_method_preventing_trait_object<F>(self: &Self) where F: TypeIdentity<Type = Self>, { } } impl<T: ?Sized> TypeIdentity for T { type Type = T; } /// A type-level identity function pub type TIdentity<Type> = <Type as TypeIdentity>::Type;