rust generics specialization

"Type annotations needed" and ICE with const generics and ... was it obvious that it exists and was missing Yes, as I said, Rust has array types that have an integer in their type signature [T; N] ; it was very awkward that this was a special case that isn't actually supported properly in the . () attempts to add additional trait bounds to a generic type. The cases that are still linted make no sense IMO. 18KB 165 lines. It's no prettier than C++ (which is to say, not very pretty), but since Rust doesn't support specialization, you'll find the compiler rejects all such generic impls that could possibly overlap. nikomatsakis commented on Feb 23, 2016 •edited. rust - How can I specialize a method for a specific ... Generic trait and specialization - help - The Rust ... bee_rider on Sept 11, 2020 [-] Swift is 6 years old, Rust might have been popular among programming language connoisseurs at the time, but it wouldn't have been that silly to expect it to be a fad. Generic trait and specialization - help - The Rust ... However, the difference which is essential one is the generic specialization in Swift is the detail of implementation, whereas Rust uses the monomorphiztions it. rust traits specialization generic-function. Define shared behavior with traits 3 min. [feature (specialization)] crate attribute. This is a tracking issue for specialization ( rust-lang/rfcs#1210 ). In Rust, "generic" also describes anything that accepts one or more generic type parameters <T>. However, just as with generic specialization, this is a best-effort optimization and is not guaranteed to actually take place. Specialization is apparently in the works. Rust vs Swift: The Key Differences You Should Know The usage of const-generic types with specialization started to cause errors since nightly-2020-05-20 (rustc 2020-05-19). All the following samples build successfully and work with nightly-2020-05-19 toolchain (rustc 2020-05-18) and earlier. Use iterators 4 min. Syntax is highly volatile and subject to change. a6b514c. This module is part of these learning paths. The cases that are still linted make no sense IMO. I want to define a trait A. I can fulfill A on anything which is a std::default::Default but I want a special implementation for u64. Support Generic. Apr 24, 2021. Introduction 1 min. Experimental specialization macros. Rust generics are sometimes called "principled" because they have to work in principle (upon declaration), not just in practice (once instantiated). Use the derive trait 5 min. But also, beyond that, this is pretty much the last major feature that I've wanted in Rust. At least currently on stable, something implements a trait or a trait method if and only if it meets all the requirements in the trait definition. It does . About a year ago I was bitten by the PL bug. Rust missing const generics has been one of the major complaints that people coming from C++ have had about Rust. Rust Issue: rust-lang/rust#31844 Summary This RFC proposes a design for specialization, which permits multiple impl blocks to apply to the same type/trait, so long as one of the blocks is clearly "more specific" than the other. You cannot specialize generics in Rust like specializing templates in C++. There are 'only' 3 things I'm waiting for: specialization. Shepmaster. At the same time, I was reading the Rust book and trying to understand the concepts there. For example, the following defines the type Point as a synonym for the type (u8, u8), the type of . SIMD. However, the primary difference is the generic specialization in Swift is an implementation detail, whereas Rust uses monomorphization for specializing the generic entirely. You are trying to specialize a method defined in an inherent impl, rather than specializing a method defined in a trait.This appears to not be supported at the moment, even after adding default to the "non special" length method.RFC 1210 mentions inherent impls as a possible extension, which I understand as not being considered for implementation at the moment. Feature Name: specialization; Start Date: 2015-06-17; RFC PR: rust-lang/rfcs#1210 Rust Issue: rust-lang/rust#31844 Summary. The following does not work either… use std::fmt::Debug; #[derive(Debug)] struct SGen<T: Debug>(T); // Generic type `SGen`. () constrain! 2. Rust probably does not support partial specialization (and operator overloading). flip1995 pushed a commit to flip1995/rust that referenced this issue on Apr 22. −. ] it's a bug). 305k 59 59 gold badges 825 825 silver badges 1085 1085 bronze badges. Please read with your own judgement! C# generics support both models: value types (structs) are monomorphized as in C++ and Rust while reference types (classes) are implemented with a polymorphic model much like Java. There are 2 specialization related features specialization and min_specialization in Rust. Generics is the topic of generalizing types and functionalities to broader cases. 1.0.0. Improve this question. This crate implements auto(de)ref specialization: A trick to do specialization in non-generic contexts on stable Rust.. For the details of this technique, see: The use of these macros requires an unstable rust compiler and the #! Specialization: Rust wishes for sound specialization of functions, and to the best of my knowledge all proposals to date ultimately fell short. RFC 2000: Const generics: which will enable non-type generic parameters, RFC 2000: Specialization on const generics. Follow asked Dec 26 '15 at 12:10. The example is to present contrast between what a specialized and unspecialized impl looks like and to point out why <T> must be used twice in a generic impl which is not necessarily obvious.. A workaround is to leave the type generic and specialize all the impls without providing a generic impl: playpen.. Other features (tbh - including async) were, for me, just nice to have additions. Use trait bounds and generic functions 4 min. At least currently on stable, something implements a trait or a trait method if and only if it meets all the requirements in the trait definition. On stable Rust, we'll need some other mechanism to accomplish specialization. This is extremely useful for reducing code duplication in many ways, but can call for rather involved syntax. All the following samples build successfully and work with nightly-2020-05-19 toolchain (rustc 2020-05-18) and earlier. Generic and Specialization in Rust. The following does not work either… use std::fmt::Debug; #[derive(Debug)] struct SGen<T: Debug>(T); // Generic type `SGen`. min_specialization implements only a subset of specialization but is more stable. I only have a little thought on Rust 2021, not worth a separate blog post I guess. Your example doesn't use the specialization feature, and the nightly specialization feature is known to have holes. [feature(specialization)] crate attribute. The usage of const-generic types with specialization started to cause errors since nightly-2020-05-20 (rustc 2020-05-19). Rust missing const generics has been one of the major complaints that people coming from C++ have had about Rust. Tracking issue: rust-lang/rust#31844. The good news is that Rust implements generics in such a way that your code doesn't run any slower using generic types than it would with concrete types. Macro to specialize on the type of an expression. This feature is unstable and requires a nightly build of the Rust toolchain. Tracking issue: rust-lang/rust#55149. )Rust generics are sometimes called "principled" because they have to work in principle (upon declaration), not just in practice (once instantiated). The example is to present contrast between what a specialized and unspecialized impl looks like and to point out why <T> must be used twice in a generic impl which is not necessarily obvious.. A workaround is to leave the type generic and specialize all the impls without providing a generic impl: playpen.. Exercise - Implement a generic type 4 min. BSD-2-Clause. Type aliases are declared with the keyword type. generators. This RFC proposes a design for specialization, which permits multiple impl blocks to apply to the same type/trait, so long as one of the blocks is clearly "more specific" than the other. asked Jan 7 '18 at 9:18. Major implementation steps: Land #30652 =) Restrictions around lifetime dispatch (currently a soundness hole) default impl ( #37653) Integration with associated consts. Rust has another language feature capable of doing this: method resolution autoref. .NET has full specialisation and dynamic linking, but sacrificed backwards compatibility and multi-language support. Auto merge of rust-lang#7059 - camsteffen:filter-map, r=flip1995. () attempts to add additional trait bounds to a generic type. The use of these macros requires an unstable rust compiler and the #! The compiler's rule is that if a method can be dispatched without autoref then it will be. constrain! Syntax is highly volatile and subject to change. 8,565 3 3 gold badges 57 57 silver badges 132 132 bronze badges. Your example doesn't use the specialization feature, and the nightly specialization feature is known to have holes. Every value has a single, specific type, but may implement several different traits, or be compatible with several different type constraints. What are generic data types? Follow edited Jan 7 '18 at 15:34. Both of them are unstable currentlly. The more specific impl block is used in a case of overlap. Tips and Traps¶ There are 2 specialization related features specialization and min_specialization in Rust. Generics. [src] Primitive traits and types representing basic properties of types. Note that this feature requires Rust 1.49. () constrain! Tracking issue: rust-lang/rust#34761 1. Rust should have specialization eventually, but there are some serious unsolved soundness problems with the current prototype. Sort of. Kornel Kornel. specialization is used to provide optimized implementations for specific T, like for example floats and integers. [feature (specialization)] trait A {} impl<T: std::default::Default> A for T {} impl A for u64 {} fn main () {} nikomatsakis commented on Feb 23, 2016 •edited. These are the only things that I ever missed. Things on this page are fragmentary and immature notes/thoughts of the author. Alex Zhukovskiy Alex Zhukovskiy. 8. const generics. "Generic type parameters" are typically represented as <T>. The simplest and most common use of generics is for type parameters. spez. Rust types can be classified in various useful ways according to their intrinsic properties. I am also been a big fan of Emacs, and this started to get me interested in how it's interpreter works. This means that there is potentially no space overhead compared to Vec . generics rust template-specialization. Vectors provide generic math operations for any T that implements that operation. Template Template Paramters (template <template <T> class X> class Y;): Rust would favor GATs instead (Generic Associated Types); I believe the RFC accepted, but implementation has not started. 3 min. was it obvious that it exists and was missing Yes, as I said, Rust has array types that have an integer in their type signature [T; N] ; it was very awkward that this was a special case that isn't actually supported properly in the . Rust accomplishes this by performing monomorphization of the code that is using generics at compile time. Take your first steps with Rust. [. Okay, I think I jumped the gun on this one. Note: it is unclear how advanced the specialization will be; in this specific case where you use full specialization it should be enough, however it is not clear whether partial specialization will be implemented, and how. Rust probably does not support partial specialization (and operator overloading). For details, see the Rustonomicon. specialize - Rust Crate specialize [ − ] [src] [ −] Experimental specialization macros. Specialization is apparently in the works. flip1995 pushed a commit to flip1995/rust that referenced this issue on Apr 22. constrain! It is suggested that you use min_specialization as specialization is disabled by Rust at this time. As far as I remember, there were plans to close . The more specific impl block is used in a case of overlap. marker. (Rust has a feature called "specialization", but it only applies to impl s, and it's not really relevant here.) This is a tracking issue for specialization ( rust-lang/rfcs#1210 ). A type alias defines a new name for an existing type. In Swift, the support for generics is a similar one to the Rust. The specialization feature is designed to do this, and the following code compiles fine: #! This is a deliberate choice on the part of Rust's designers to . Note that smallvec can still be larger than Vec if the inline buffer is larger than two machine words. (Rust has a feature called "specialization", but it only applies to impls, and it's not really relevant here. 93.2k 32 32 gold badges 207 207 silver badges 290 290 bronze badges. However, because const generics are not a first class feature, users cannot define their own types which are generic over constant values, and cannot implement traits for all arrays. To use this feature add features = ["union"] in the smallvec section of Cargo.toml. C++ and Rust have full value types and template specialisation, but not dynamic linking of the results (see a discussion of the problems Rust faces with that). This feature makes the Rust compiler less strict about use of vectors that contain borrowed references. Share. Major implementation steps: Land #30652 =) Restrictions around lifetime dispatch (currently a soundness hole) default impl ( #37653) Integration with associated consts. #396 in Rust patterns. The support for generics in Swift is similar to Rust. It started with reading Crafting Interpreters and discovering the wonders hidden under the hood of a compiler. const generics are used to enable Vectors to contain any (fixed) number of elements and therefore not require allocation on the heap. Both of them are unstable currentlly. Deprecate `filter_map` Since rust-lang#6591, `filter_map` does not even lint `filter ().map ()`. Share. A type parameter is specified as generic by the use of angle brackets and upper camel case: <Aaa, Bbb, .>. Okay, I think I jumped the gun on this one. a6b514c. You cannot specialize generics in Rust like specializing templates in C++. These classifications are represented as traits. Deprecate `filter_map` Since rust-lang#6591, `filter_map` does not even lint `filter ().map ()`. But again, C# doesn't have specialization. See also C++ vs C: Learn About the Main Differences between These. Any current specialisation of a generic function is a quirk that probably isn't actually meant to work (i.e. Auto merge of rust-lang#7059 - camsteffen:filter-map, r=flip1995. I've got some long-form writing in my head about this, but previously, I would have cast it as two or 2.5 features: * const generics * GATs * specialization (this is the half) may_dangle. Namely, being generic requires taking great care to specify over which types a generic type is actually considered valid. Rust currently has one type which is parametric over constants: the built-in array type [T; LEN].
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