// Copyright 2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. use std::fmt; use std::iter::FromIterator; use std::slice; // Note 1: It is not clear whether the flexibility of providing both // the `Growable` and `FixedLen` variants is sufficiently useful. // Consider restricting to just a two variant enum. // Note 2: Once Dynamically Sized Types (DST) lands, it might be // reasonable to replace this with something like `enum MaybeOwned<'a, // Sized? U>{ Owned(Box), Borrowed(&'a U) }`; and then `U` could be // instantiated with `[T]` or `str`, etc. Of course, that would imply // removing the `Growable` variant, which relates to note 1 above. // Alternatively, we might add `MaybeOwned` for the general case but // keep some form of `MaybeOwnedVector` to avoid unnecessary copying // of the contents of `Vec`, since we anticipate that to be a // frequent way to dynamically construct a vector. /// MaybeOwnedVector<'a,T> abstracts over `Vec`, `~[T]`, `&'a [T]`. /// /// Some clients will have a pre-allocated vector ready to hand off in /// a slice; others will want to create the set on the fly and hand /// off ownership, via either `Growable` or `FixedLen` depending on /// which kind of vector they have constructed. (The `FixedLen` /// variant is provided for interoperability with `std::slice` methods /// that return `~[T]`.) pub enum MaybeOwnedVector<'a,T> { Growable(Vec), FixedLen(~[T]), Borrowed(&'a [T]), } /// Trait for moving into a `MaybeOwnedVector` pub trait IntoMaybeOwnedVector<'a,T> { /// Moves self into a `MaybeOwnedVector` fn into_maybe_owned(self) -> MaybeOwnedVector<'a,T>; } impl<'a,T> IntoMaybeOwnedVector<'a,T> for Vec { #[inline] fn into_maybe_owned(self) -> MaybeOwnedVector<'a,T> { Growable(self) } } impl<'a,T> IntoMaybeOwnedVector<'a,T> for ~[T] { #[inline] fn into_maybe_owned(self) -> MaybeOwnedVector<'a,T> { FixedLen(self) } } impl<'a,T> IntoMaybeOwnedVector<'a,T> for &'a [T] { #[inline] fn into_maybe_owned(self) -> MaybeOwnedVector<'a,T> { Borrowed(self) } } impl<'a,T> MaybeOwnedVector<'a,T> { pub fn iter(&'a self) -> slice::Items<'a,T> { match self { &Growable(ref v) => v.iter(), &FixedLen(ref v) => v.iter(), &Borrowed(ref v) => v.iter(), } } } // The `Vector` trait is provided in the prelude and is implemented on // both `&'a [T]` and `Vec`, so it makes sense to try to support it // seamlessly. The other vector related traits from the prelude do // not appear to be implemented on both `&'a [T]` and `Vec`. (It // is possible that this is an oversight in some cases.) // // In any case, with `Vector` in place, the client can just use // `as_slice` if they prefer that over `match`. impl<'b,T> slice::Vector for MaybeOwnedVector<'b,T> { fn as_slice<'a>(&'a self) -> &'a [T] { match self { &Growable(ref v) => v.as_slice(), &FixedLen(ref v) => v.as_slice(), &Borrowed(ref v) => v.as_slice(), } } } impl<'a,T> FromIterator for MaybeOwnedVector<'a,T> { fn from_iter>(iterator: I) -> MaybeOwnedVector { // If we are building from scratch, might as well build the // most flexible variant. Growable(FromIterator::from_iter(iterator)) } } impl<'a,T:fmt::Show> fmt::Show for MaybeOwnedVector<'a,T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.as_slice().fmt(f) } } impl<'a,T:Clone> CloneableVector for MaybeOwnedVector<'a,T> { /// Returns a copy of `self`. fn to_owned(&self) -> ~[T] { self.as_slice().to_owned() } /// Convert `self` into an owned slice, not making a copy if possible. fn into_owned(self) -> ~[T] { match self { Growable(v) => v.as_slice().to_owned(), FixedLen(v) => v, Borrowed(v) => v.to_owned(), } } } impl<'a,T:Clone> MaybeOwnedVector<'a,T> { /// Convert `self` into a growable `Vec`, not making a copy if possible. pub fn into_vec(self) -> Vec { match self { Growable(v) => v, FixedLen(v) => Vec::from_slice(v.as_slice()), Borrowed(v) => Vec::from_slice(v), } } }