Rust repr macro It also reexports the tstr crate unconditionally, to use its TS macro as the type parameter of the GetFieldOffset trait. Outer attributes like #[repr(transparent)]. The full version of the README can be found on GitHub. The main difference being using some form of global state; the Python decorator, by virtue of just having to be a classic Python callable, can hold some internal state; whereas the procedural macros are executed within a special Jan 24, 2021 · Rust 参考手册是 Rust 官方编写的 Rust 语言规范手册，由于语言还在快速迭代当中，所以本手册的内容还未固定下来。但这是一本学习和了解 Rust 全面的语言特性必不可少的书籍。 Apr 5, 2020 · One way to determine whether changing a repr(C) struct to repr(C, packed) will lead to UB is to create two similar structs, one repr(C) and the other repr(C, packed), and to compare their sizes. The alignment of a value specifies what addresses are valid to store the value at. I'm looking for feeback. repr 0. This enables you to perform round trip style conversions from enum into string and back again for unit style variants. Motivation Enums with the #[repr(u*)] or #[repr(i*)] attributes are commonly used for wrapping primitive integer values accepted by, or returned from, an underlying library when doing FFI. There are two varieties of Rust macro: macros by example and procedural macros. The struct itself has to be marked with the #[repr_std140] attribute: this ensures the rust compiler will correctly order and align the fields. derive, repr) are applied to it. The doc says: Mar 16, 2017 · The difference you see in the output of your program is not due to memory layout. For example, if you have an unsafe function that requires a specific repr, you can use these traits to create a safe wrapper around it. macro_export — Exports a macro_rules macro for cross-crate usage. derive type macro give you the information about fields in enum/struct/union. Jul 12, 2021 · Rust should do the right thing if you just copy a field value. repr traits wrappers Macros§ and Pi c Pattern from a char delimit Delimit pattern by e Escaped character i Interval or Sigma p Pattern xor Delta Structs§ Context Interval Seq When writing bindings for C libraries which use enums there are a few options for declaring rust versions of C enums. Rust doesn't have a complete specification, but the repr attribute is mentioned in the Rust reference , so it is absolutely a part of the language. You can specify visibility like this: This library maintains support for rust compiler versions that are 4 minor versions away from the current stable rust compiler version. pub use crate::repr::Repr; pub use traits::Integral; pub use crate::repr::Repr::*; Modules§ constants macros Macro definitions. Use a rust enum. If it is important for a generic parameter to have a particular repr, you can use the traits in this crate to ensure that it has the needed repr. As @2e71828 pointed out, their mechanisms are very different. A value of alignment n must only be stored at an address that is a multiple of n. The macros provied by this crate are also available by enabling the derive feature in aforementioned strum crate. It's even possible to specify the numeric value for each variant, if they don't contain data: enum Foo { Bar = 0, Baz = 1, Quux = 42, } 6 days ago · If layout stability is required, consider using an explicit repr attribute. After reading the "Type layout" chapter (especially "The Rust Representation" section) of Rust Reference, I'm still confused about how exactly Rust makes data layout. repr-0. But in practice, you can achieve very similar things with both. 2 Permalink Docs. , here is the spl-token program source code). For GLSL primitive types, compatibility is defined by the following mapping from GLSL types to std140 types: The Derive Macro. Example: Generate enum repr conversions compatible with type aliases. However, two different compilations of the same program may result in different layouts. Playground: Rust Playground // Author: Volodymyr M. Rust has six types of attributes. Functions generated are ⓘ Dec 26, 2019 · You "just" have to manually parse what represents the syntax of an enum definition: a comma-separated sequence of variant names, where each may be followed by a parenthesized comma-saparated sequence of types (technically braces with named fields are a possibility too, but handling both within the same macro would require making it much more complex), and both sequences accept trailing commas: Nov 10, 2022 · I'm trying to convert an unsigned integer to an enum. For example, if you have at most 256 variants, you can use #[repr(u8)], so the enum is guaranteed to be a u8. 0 Links; Homepage Macros § and. This crate only contains derive macros for use with the strum crate. There is no standard way, for example, to get a list of all variants of a C-like enum. 46. Aug 7, 2023 · The title says it all: is it possible with a procedural macro (derive) on a structure to check whether the structure is repr(C)? Aug 22, 2020 · repr(Rust) enums should be free of any integer-layout constraint, so I wouldn't expect that conversion to be available even if this TryFrom was built-in. 0 . As a workaround, I wrote the enum_primitive crate, which exports a macro enum_from_primitive! that wraps an enum declaration and automatically adds an implementation of num::FromPrimitive (from the num crate). proc_macro — Defines a function-like macro. #[repr(transparent)] pub struct AbsoluteSystemPath(Path); // Made up syntax, not the point of this conversation. This crate provides the UnitEnum derive macro which automatically implements various utility methods for working with enums. Rust 确实保证 A 的两个实例具有完全相同的数据布局。 但是，Rust 目前 不 保证 A 的实例与 B 的实例具有相同的字段顺序或填充。 对于如上编写的 A 和 B，这一点似乎有点吹毛求疵，但 Rust 的其他几个特性使得该语言以复杂的方式处理数据布局是可取的。 Dec 7, 2020 · @Alvra, by macro_rules you can't know about enum fields. decorators. Within the state_machine macro you must define at least one state transition. Rust 参考手册是 Rust 官方编写的 Rust 语言规范手册，由于语言还在快速迭代当中，所以本手册的内容还未固定下来。但这是一本学习和了解 Rust 全面的语言特性必不可少的书籍。 Jun 26, 2024 · Ask questions, find answers and collaborate at work with Stack Overflow for Teams. 5. I was hoping for a conversion like: fn uint_to_enum<U, E>(uint: U) -> E { unsafe { std::mem::transmute(uint) } } where E is the enum and U is the unsigned type it uses in the repr attribute. This allows multiple macros to process the same item. #[derive A procedural macro for enhancing enums that consist primarily of unit variants. 0 then we will guarantee support up to and including 1. Macro definitions. Use a raw integer and a bunch of constants. In the following example, surrounding the matcher with $(),+ will match one or more expression, separated by commas. The enum will have #[repr(<size here>)] with any of the unsigned integer types. Explore Teams Macros. macro_use — Expands macro visibility, or imports macros from other crates. These appear inside of the item they describe, usually a module. Jan 6, 2025 · The principle of #[repr(C)] structs remains the same. impl Path for AbsoluteSystemPath { /* allow-list or deny-list of stuff */ } This could allow the newtype to reuse all of the impl s from the inner type, and possibly for bonus points, those previously unimplementable because of the Converts enum variants to strings. Deriving Display on an enum prints out the given enum. In searching for solutions, I finally came across this thread. §Attempting to turn a primitive into an enum with try_from Generates minimalistic, pure, safe rust functions; Compile-time checks for type and field sizes; Rust-analyzer/docrs friendly (carries over docs to accessor functions) Exports field offsets and sizes as constants (useful for const asserts) Generation of Default, fmt::Debug, or defmt::Format traits; Custom internal representation (endianness) May 7, 2023 · Proc-macro crate for 'isrepr' crate Rust guarantees that the layout of a struct is compatible with the platform's representation in C only if the #[repr(C)] attribute is applied to it. A value with alignment n must only be stored at an address that is a multiple of n. Dec 17, 2020 · 警告：C语言中的枚举与 Rust 中的那些应用了 #[repr(C)]表型的无字段枚举之间有着重要的区别。 C语言中的枚举主要是 typedef 加上一些具名常量；换句话说，C枚举(enum)类型的对象可以包含任何整数值。 Rust library for safely validating and converting arbitrary memory to #[repr(C)] Rust types - Samsung/rust-repr §Dependencies. Use a newtype and a set of constants. All of them have use cases for which they are valid: Rust enums work when calling from rust code into C code. For example, a value with an alignment of 2 must be stored at an even address, while a value with an alignment of 1 can be stored at any address. It respects the enum’s #[repr] attribute for discriminant types and provides methods for accessing variant names, ordinals, and discriminants. Inner attributes like #![feature(proc_macro)]. proc_macro_attribute — Defines an attribute macro. Rust guarantees that the offset of a given field within a given type will not change over the lifetime of the program. If the API needs to be convenient, you can implement a derive proc macro that implements the unsafe trait when it can prove that it's safe to do so - e. rs crate page MIT/Apache-2. This means that the ABI of a &MySlice<T> is the same as that of a &[T], since MySlice has no other fields, and we can therefore treat it the same as [T]. give the compiler the opportunity to avoid memcpy operations Jul 5, 2024 · Suppose I have a type MyEnumVariantGen which impl IntoIterator<Item=(String,u8)>, I can write a proc macro to generate variants for #[repr(u8)] enum MyEnum. Jan 1, 2021 · If violating the contract can cause UB, then the marker trait should be an unsafe trait, so it must be implemented in an unsafe block. I'm primarily looking for feedback on soundness, although I also want to get the efficiency as high as possible (ie. when it finds #[repr(packed)] among the type attributes. my_int } } pub fn g() -> u32 { let ms = MyStruct { my_int: 0 }; ms. Lisivka <vlisivka@gmail. Diagnostics Strum is a set of macros and traits for working with enums and strings easier in Rust. §Including Strum in Your Project. The bitmask! macro creates a struct and an enum that holds your flags. 2. repr(Rust) First and foremost, all types have an alignment specified in bytes. Currently this library is geared toward use in Rust procedural macros, but contains some APIs that may be useful more generally. macro_attr_callback: This macro invokes a "callback" macro, merging arguments together. For example, if the current stable compiler version is 1. 50. Rust website The Book Standard Library API Reference Module repr:: macros Copy item path source · [−] Expand description. If you have many enums which you want to print, you can write a trivial macro to generate the above implementation of Display for each of them. strum_macros contains the macros needed to derive all the traits in Strum. 可选的数据布局. md")] x: u32 } You can specify the representation with #[repr]. 0. #[repr(C)] can also be applied to an enum. Safety: Interfacing with C/C++ bypasses some of Rust's safety checks, such as borrow checker, so be thorough with unsafe code audits. Docs. Adding an explicit repr(u*), repr(i*), or repr(C) to an enum with fields suppresses the null-pointer optimization, like: #![allow(unused)] fn main() { use std::mem::size_of; enum MyOption<T> { Some(T), None, } #[repr(u8)] enum MyReprOption<T> { Some(T), None, } assert_eq!(8, size_of::<MyOption<&u16>>()); assert_eq!(16, size_of::<MyReprOption Apr 24, 2021 · #[repr(C)] is not a preprocessor directive, since Rust doesn't use a preprocessor 1. Fields only have a single constraint: they have to implement Copy. The Traits to represent reprs. Nov 3, 2018 · Summary Add conversion to and from underlying integer type on enums with the #[repr(u*)] or #[repr(i*)] attribute. I think the current requirement of num_enum is quite honest: the enum needs an explicit #[repr({integer})] annotation: Macros can use + in the argument list to indicate that an argument may repeat at least once, or *, to indicate that the argument may repeat zero or more times. I was reading Procedural Macros - The Rust Reference #[repr(C)] struct A{ element: Vec<u32>, sentence: String, another: f64 } into its serialized variant struct ArchivedA{ element: [u32;Y], sentence: [char;X], another: [u8;Z] // retrieve using from_bits to_bits } with X, Y and Z the dynamic size of the elements with eventual According to The Rust Reference, the single field of the struct with the #[repr(transparent)] will have both the same representation and ABI. Jun 19, 2022 · What I'd really like to do is run a macro (or something) to take a packed C-struct and generate a "regular" Rust struct from it. toml. Unfortunately, in Rust reflective programming is somewhat difficult. Aug 22, 2024 · A macro that can take arguments once, and generate all possible combinations of them. Here is my PoC. c Feb 14, 2024 · However, I see lots of #[repr(C)] in Solana Program Library (e. Pi. The alignment of a type specifies what addresses are valid to store the value at. Since the repr(C) s prevent Rust from reordering the fields, if the two are of equal size then there is no padding within the packed struct , though Oct 11, 2023 · Rust是一门现代的、安全的系统级编程语言，它提供了丰富的元编程特性，其中属性宏（Attribute Macros）是其中之一。属性宏允许开发者在代码上方添加自定义的属性，并对代码进行定制化处理。在本篇博客中，我们将深入探讨Rust中的属性宏，包括属性宏的定义、使用方法以及一些实际应用案例，以 A bitmask generator for enum scoped bit flags. The enum contains all the bit flag variants and the struct is a mixture of those bit flags called a bitmask. The web page explains the concepts of alignment, size, padding, and field order, and gives examples of different cases and optimizations. Preferably the From trait will be implemented both ways so it'll copy it back and forth. Practical Considerations. Generate with #[EnumRepr(type = "TYPE")]. Jul 9, 2023 · Background: This is something I wrote based on the need described here: A way to return stack-allocated #[repr(Rust)] types to C through FFI? I plan to publish it once it gets some more eyes for safety / soundness. proc_macro_derive — Defines a derive macro. The DynStruct macro can be applied to any #[repr(C)] struct that contains a dynamically sized array as its last field. Types supported: I support 3 types of units: &'static str, String, and Cow. Note that if the attribute appears within another macro, it will be expanded after that outer macro. Learn how Rust lays out composite data types such as structs, tuples, arrays, enums, and unions, and how to use the repr macro to control the layout. An attribute, like #[repr(transparent)]. This library re-exports the ReprOffset derive macro from the repr_offset_derive crate when the “derive” feature is enabled, this is disabled by default. Aug 1, 2020 · Attribute macros vs. Rust 允许你指定不同于默认的数据布局策略，并为你提供了不安全代码指南。. But, if I want to generate variants for enum MyEnum2 with MyEnum2VariantGen, I'd have to clone & modify the existing macro, and the implementations of both MyEnumVariantGen and MyEnum2VariantGen must live in the proc macro crate, not the API documentation for the Rust `repr` crate. The macro adds from_repr(discriminant: usize) -> Option<YourEnum> as a standalone function on the enum. num_enum’s IntoPrimitive is more type-safe than using as, because as will silently truncate - num_enum only derives From for exactly the discriminant type of the enum. Example ⓘ 但是，这仅适用于作为标准库的一部分提供的特征; 它不可定制。 但是现在，当有人想要推导出你的特质时，你可以告诉Rust要做什么。 这在serde， Diesel等流行的crate中大量使用。 获取更多信息，包括如果构建你自己的derive，查阅 Syn is a parsing library for parsing a stream of Rust tokens into a syntax tree of Rust source code. get_my_int() } Macros. Import strum and strum_macros into your project by adding the following lines to your Cargo. Jun 19, 2019 · I'm trying to implement safe c-like enum's for Rust, because I'm hurt by incompatibility between C enum's and Rust #[repr(C)] enum's. If you want to transmute a single-field struct and have it guaranteed to never become UB in the future, you need to mark the struct #[repr(transparent)] or #[repr(C)]. §Visibility. . macro_attr: When given an item definition, including its attributes, this macro parses said attributes and dispatches any attributes or derivations suffixed with ! to user-defined macros. Using that you can generate any piece of code. Jan 20, 2015 · std::num::FromPrimitive is marked as unstable and will not be included in Rust 1. (Future possibility: my info is (or becomes) out of date, and single-field #[repr(Rust)] structs are guaranteed to be transmute-compatible with their single field type. com> pub trait IsEnumValid { fn is_value_valid(repr: i32) -> bool; } /// The wrapper for C-like enum, which has same size as C enum. Box<T> heap allocates and stores a pointer to the heap contents, so what you are printing is the pointer. This macro adds a standalone function to obtain an enum variant by its discriminant. #[repr(C, packed)] can be used to lay out struct members without padding. rs. It is therefore safe to convert between them. repr(C) 这是最重要的 repr。它的意图非常简单：按照 C 的方式处理数据。 Jun 7, 2022 · I have the following rust type: enum SmallPrime { Two = 2, Three = 3, Five = 5, Seven = 7, } I can deserialize using json: [ 2, 3, 5, 7 ] use serde_repr::*; #[derive Strum is a set of macros and traits for working with enums and strings easier in Rust. The former are simpler and most common; they look like function calls and Jun 26, 2024 · ONLY IF the repr attribute, when present, is guaranteed to be the first attribute. g. §Syntax. Tooling: Tools like rust-bindgen can automatically generate Rust bindings for existing C/C++ code. Also note that the semicolon is optional on the last case. Rust provides an extremely powerful macro system. As such, it becomes a very common task to convert these Rust enum variants to their Note that if there is no outputs in the specification, the output alphabet is an empty enum and due to technical limitations of many Rust attributes, no attributes (e. So alignment 2 means you must be stored at an even address, and 1 means that you can be stored anywhere. These appear outside or in front of the item they describe. While the C preprocessor operates almost directly on the text of your source code, the Rust macro system operates at a higher level. For example, the following code will expand the Serialize proc-macro first, which must preserve the include_str! call in order for it to be expanded: #[derive(Serialize)] struct Foo { #[doc = include_str!("x. (Playground - I examined asm and llvm output) #[repr(C, packed)] struct MyStruct { my_int: u32, } impl MyStruct { #[inline(never)] pub fn get_my_int(&self) -> u32 { self. Dec 8, 2024 · Hi, The end goal is to serialize this struct, ala rkyv or serde. Outer one-line doc comments like /// Example. technically, it's possible to write a declarative macro to parse what's in your original example (more or less), but it's usually very complicated and not worth the effort to make it able to parse the complete syntax. For variants with additional data, the returned variant will use the Default trait to fill the data. It is an attribute . gofzn xfjx btxd gqih zauetu jcirw uiqpp infkyp smxzw mteyv tkfey bao semno eebm vdrscxm