Rust Repr I32, Shifts the bits to the left by a specified amount
Rust Repr I32, Shifts the bits to the left by a specified amount, n, wrapping the truncated bits to the end of the resulting integer. Using this representation explicitly through a repr attribute is guaranteed to be the same as omitting the 可选的数据布局 Rust 允许你指定不同于默认的数据布局策略。 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。字段的顺序、大小和对齐方式完全符合你对 C 或 C++ 的预期。该 Rust will consequently insert padding where necessary to ensure that all fields are properly aligned and that the overall type's size is a multiple of its alignment. If u* or i* types are used for the discriminant, the actual enum representation is made to be #[repr(that_type_specified)]. Here’s what really happens when Redundant constants module for the i32 primitive type. The enum type isn’t used directly as a field, because the Protobuf spec mandates that enumerations This page gives an overview of all public Series methods. The list of The real enum discriminant is usually forced to be #[repr(isize)]. The real enum discriminant is usually forced to be #[repr(isize)]. The boolean type. The list of types recognized as u* and i* currently is as follows: i8, i16, On second thoughts, adapting MyEnum to enum MyEnum { A = 1, B, C, Other(i32) } is probably a better solution for my problem. The 32-bit signed integer type. Rust by Example (RBE) is a collection of runnable examples that illustrate various Rust concepts and standard libraries. Motivation Enums with the #[repr(u*)] or #[repr(i*)] attributes are commonly used for set_property is where we get issues with Attribute::Athletics as i32 I proposed one way to do it: in set_property generate a const ATHELTICS_I32_VAL : i32 = Attribute::Athletics as i32; and match The control over the current thread is switched from Rust to C to Rust for the execution of the callback, but in the end the callback is executed on the same thread that called the function which triggered Rust has attempted to support a semantics for enum discriminant representation where, if you did not choose an explicit enum representation, it would infer the appropriate representation to use. In addition to defining a type, it also defines a constructor of the same name in the value namespace. # [repr (C)] pub struct MyStruct1 { value1: i32, value2: i32, } → 構造体を他言語から使用できるようにする 另外团队中使用了一些调用 C 库 lib，比如 rust-rocksdb 库，里面封装 C 的数据结构会频繁出现 # [repr (C)]。 本文是在以上两个问题引申下展开的，学习探讨下 Rust 数据类型的内存布局。 主要分为两个 Rust by Example (RBE) is a collection of runnable examples that illustrate various Rust concepts and standard libraries. A tuple struct is a nominal tuple type, and is also defined with the keyword struct. The list of (That includes this function specifically, integer-to-pointer casts, and helpers like dangling, but also semantically-equivalent conversions such as punning through repr(C) union fields. rs. However Rust does not currently guarantee that an Thanks for your input @euphbriggs! However, I believe that syntax is only usable in query_as!() macro, not so much in the method. The enum will have #[repr(<size here>)] with any of the unsigned integer types. So far I've figured out how #[repr(Rust)] and #[repr(C)] differ: #[repr(Rust)] is a default behavior while initializing, for an 在这个例子中： #[repr(i32)] 属性告诉编译器这个枚举应该使用 i32 类型来存储其值。 StatusCode 枚举有三个变体，每个变体都被赋予了一个固定的 i32 类型的值。 在 main 函数中，通过类型转换（例如 What `# [derive (TryFrom)]` generates What #[derive(TryFrom)] generates Derive TryFrom allows you to convert enum discriminants into their corresponding variants. Quick google search yielded this solution: https://stackoverflow. Some(&T)) makes If u* or i* types are used for the discriminant, the actual enum representation is made to be #[repr(that_type_specified)]. The bool represents a value, which could only be either true or false. However Rust does not currently guarantee that an The returned value has the same type as self, and will be interpreted as (a potentially different) value of a native-endian i32. However Rust does not currently guarantee that an instance of A has the same field ordering or padding as an const ATHELTICS_I32_VAL : i32 = Attribute::Athletics as i32; and match against that. This would be the return type of The Rust representation is the default representation for nominal types without a repr attribute. The constructor is a Rust程序内存布局涉及存储宽度、对齐位数等核心参数，影响FFI跨语言互操作及内存空间利用率。自定义数据结构内存布局包括对齐、大小等属性，编译器通过优化字段顺序减少填充位。Rust与C内存布 repr (C) は「C 言語と互換性を持つ」なので int 型と同じサイズになるかと思いますが、 C の int 型は 処理系依存 なのでちょっと曖昧な感じがします。 "Primitive representations" は "repr (整数型名)" Luckily, repr(C) newtypes are laid out just like the type they wrap on all platforms which Rust currently supports, and likely on many more. However Rust does not currently guarantee that an instance of A has the same field ordering or padding as an struct A { a: i32, b: u64, } struct B { a: i32, b: u64, } Rust does guarantee that two instances of A have their data laid out in exactly the same way. That is both efficient and portable, giving the same result on both little-endian and big-endian systems. rotate_left(n) is equivalent to applying rotate_left(1) a total of n struct A { a: i32, b: u64, } struct B { a: i32, b: u64, } Rust 确实 保证 A 的两个实例的数据布局方式完全相同。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。 按照 A 和 B 的写 struct A { a: i32, b: u64, } struct B { a: i32, b: u64, } Rust 确实 保证 A 的两个实例的数据布局完全相同。然而，Rust 目前 并不 保证 A 的实例与 B 的实例具有相同的字段排序或填充。 对于我们编写的 A 和 B Another way to do it (I think) would be to just have a: #[repr(C/transparent)] struct Result(i32); that implements From<std::result::Result> and Into<std::result::Result>. None) and a (potentially nested) non- nullable pointer variant (e. However, all of their constituent types already do have guaranteed layouts. There's also the unsafe code guidelines (note that it's NOT normative). Examples Basic usage: The 32-bit signed integer type. In this article, we will explore how these patterns are utilized, focusing Rust does guarantee that two instances of A have their data laid out in exactly the same way. The classic case of this is Rust's "null pointer optimization": an enum consisting of a single outer unit variant (e. Is there a way that I've missed that will let you do that, or does it only go one way? Alternative representations Rust allows you to specify alternative data layout strategies from the default. } Accessing discriminant Via # [repr (C)] 仅只代表最外层结构体 Data 的两个字段 id 和 name 是按 C 内存布局规格“摆放”在内存中的。 但， # [repr (C)] 并不意味着整个数据结构都是 C 内存布 I'm trying to convert an unsigned integer to an enum. If you cast a bool into an integer, true will be 1 and false will be 0. #[repr(C, packed)] struct Object { a: i32, // other members } And for detecting that the memory layout is ok, you can initialize a struct and check that the offsets are ok by casting the pointers to integers: Currently, the Arc, Rc, and Weak structs do not have a #[repr()]; they don't have a guaranteed type layout. See to_le_bytes() for a type-safe alternative. However, it is not correct, because the # [repr (i32)] attribute overrides the The largest value that can be represented by this integer type (2 31 − 1). Match statement efficiency? seems to suggest it DOES by default get compiled to jump table. Pattern Matching with Enums in Rust Pattern matching in In this article we'll dissect the implementation of std::io::Error type from the Rust's standard library. rotate_left(n) is equivalent to applying rotate_left(1) a total of n The Rust representation is the default representation for nominal types without a repr attribute. Syntactically, the repr meta list will be The 32-bit signed integer type. rotate_left(n) is equivalent to applying rotate_left(1) a total of n repr (Rust) 本书将深入挖掘Rust非安全（unsafe）编程中的一些必要但是又可怕的细节。由于此类问题天然的恐怖，本书散发出的不可描述的恐惧之力，极可能将你的神经彻底撕成千万个绝望的碎片。 struct A { a: i32, b: u64, } struct B { x: i32, b: u64, } Rust 确实 保证两个A的实例有确实相同的数据布局。 然而Rust 并不 保证一个A的实例和一个B的实例有相同字段顺序或填充（在实践中并没有特别的理由 #[repr(align = "16")] struct MoreAligned (i32); This structure will still have an alignment of 16 (as returned by mem::align_of), and in this case the size will also be 16. I'll leave the original question up for other users, Either you write out a match statement in full or use a crate to bring in a macro for it. ) Rust 中的数据表示低级编程非常关心数据布局。这是一件大事。它还普遍影响着语言的其余部分，因此我们将从深入研究数据在 Rust 中的表示方式开始。 本章在理想情况下与 参考资料的类型布局部分 // The list item struct in this example is defined in C code as: > +//! // struct SampleItemC { > +//! // int value; > +//! // struct list_head link; > +//! // }; > +//! // > +//! # [repr (transparent)] > +//! pub (crate) Rust repr (Rust) 底层编程经常需要关注数据布局。 每种类型都有一个数据对齐属性 (alignment)。 一种类型的对齐属性决定了哪些内存地址可以合法地存储该类型的值。 如果对齐属性是n，那么它的值的存 Hello 👋 How to determine, preferably before bindings generation, translated rust type of enum? On various archs and OSs it can be unsigned or signed integer (i32/u32/etc) and I need to determine it I’ve ran into an issue with FFI that I believe requires clarification, or maybe some additions to the language. The list of The boolean type. Other repr s do not apply to C-like enums. An explicit repr (inttype) would be necessary, as repr (C) is "an educated guess" and repr (rust) is "assume nothing about anything". Consider using the From repr (Rust) 本书将深入挖掘Rust非安全（unsafe）编程中的一些必要但是又可怕的细节。由于此类问题天然的恐怖，本书散发出的不可描述的恐惧之力，极可能将你的神经彻底撕成千万个绝望的碎片。 To break an i64 into two i32, I would use let (low, high) = (val as i32, (val >> 32) as i32). g. However Rust does not currently guarantee that an Converts an i32 to a Syntax, or None if value is not a valid variant. rotate_left(n) is equivalent to applying rotate_left(1) a total of n Summary Add conversion to and from underlying integer type on enums with the #[repr(u*)] or #[repr(i*)] attribute. This means that code in debug mode will trigger a panic on this case and optimized I can cast a # [repr (i32)] enum to an i32, but it doesn't let me do it in the other direction. repr (Rust) 首先，所有类型都有一个以字节为单位的对齐方式，一个类型的对齐方式指定了哪些地址可以用来存储该值。 一个具有对齐方式n的值只能存储在n的倍数的地址上。 所以对齐方式 2 意味着你必 } #[repr(u8)] enum OverflowingDiscriminantError2 { MaxMinusOne = 254, // 254 Max, // 255 MaxPlusOne // Would be 256, but that overflows the enum. repr (C) This is the most The 32-bit signed integer type. That one is easy: #[repr(C)] struct Foo(i32, i32); struct Bar(i32, i32); Here Foo is FFI-safe, I have an enum: enum Foo { Bar = 1, } How do I convert a reference to this enum into an integer to be used in math? fn f(foo: &Foo) { let f = foo as u8; // error[E0606]: casting `&am I tried to use let u8slice : &[u8] = i8slice as &[u8]; But it complains an as expression can only be used to convert between primitive types. rotate_left(n) is equivalent to applying rotate_left(1) a total of n My uncertainty comes from not understanding why a tuple struct would be OK, but a struct containing a tuple isn't. With #[repr(_)] the integer representation is used when converting from/to SQL and Memory layout refers to how data is organized in memory, which affects performance, safety, and interoperability with other languages and 代替メモリレイアウト Rust では、デフォルトとは異なる、代替のデータレイアウトを指定することができます。 repr (C) これは最も重要な repr です。意味はとても単純で、「C がやるようにやれ」 . Basic usage bool implements repr 属性的对齐方式 欢迎来到 Rust 版本 (Edition)使用指南！ "Editions" 是通过编写 Rust 代码来传达巨大改变的一种方式。在指南中，我们将讨论：什么是版本 (editions)；每个版本什么样；如何将你的 The 32-bit unsigned integer type. com/questions/28028854/how-do-i-match-enum Enums in Rust are a powerful and flexible data type that can be more explicitly expressed through patterns. Enumeration Enumerations may be defined in Rust and can match SQL by integer discriminant or variant name. The code in question is here: library/std/src/io/error. Enums By default, a TryFrom<isize> is Isize = 11 The type of the discriminant for a # [repr (isize)] enum This is the default discriminant type for repr (C). The absolute value of i32::MIN cannot be represented as an i32, and attempting to calculate it will cause an overflow. An overview of the issue proto -> rust for an enum looks like: // proto enum Purpose struct A { a: i32, b: u64, } struct B { a: i32, b: u64, } Rust does guarantee that two instances of A have their data laid out in exactly the same way. This is optimized for performance and safety within Rust itself. rotate_left(n) is equivalent to applying rotate_left(1) a total of n use num_derive::FromPrimitive; use num_traits::FromPrimitive; #[derive(FromPrimitive)] enum MyEnum { A = 1, B, C, } fn main () { let x = 2; match FromPrimitive::from 入门理解 enum定义时可以使用 #[repr(Int)] 修饰，Int就是Rust的整数类型 (u8, isize这种)。 对于C风格enum和没有变体的enum，repr定义了其需要使用对应 The 32-bit signed integer type. I was hoping for a conversion like: fn uint_to_enum<U, E>(uint: U) -> E The real enum discriminant is usually forced to be #[repr(isize)]. when The 32-bit signed integer type. 10 I'm trying to understand the difference between these three representations. repr 属性的对齐方式 Wikipedia: 现代计算机硬件中的 CPU 在数据自然对齐时，可以最有效地执行对存储器的读写，这通常意味着数据地址是数据大小的倍数。 数据对齐是指根据元素的自然对齐来对齐元 No, it doesn't work, because Rust #[repr(C)] enumerations are incompatible with C enumerations, so they are replaced by i32 by authors of Prost crate, so deserialization with Serde is not working While using #[repr(C)] ensures that Rust enums are laid out in a compatible manner with C, care must be taken to prevent invalid values from being introduced. 代替メモリレイアウト Rust では、デフォルトとは異なる、代替のデータレイアウトを指定することができます。 repr (C) これは最も重要な repr です。意味はとても単純で、「C がやるようにやれ」 This is your trusty default for structs and enums in Rust. For example, consider this C declaration: Note that the getter methods will return the Rust enum’s default value if the field has an invalid i32 value. New code should use the associated constants directly on the primitive type. From the errors that I'm getting it Write(String), ChangeColor(i32, i32, i32), } This Message enum can be in any of the four variants, with some variants holding additional data. rotate_left(n) is equivalent to applying rotate_left(1) struct A { a: i32, b: u64, } struct B { a: i32, b: u64, } Rust does guarantee that two instances of A have their data laid out in exactly the same way. Using this representation explicitly through a repr attribute is guaranteed to be the same as omitting the Here IntelliJ-Rust shows a "mismatched type" error on the Whatever enum variant definition, "expected isize, found i32 ". Another proposed solution was to use if guards instead : val if val == (Attribute::Athletics as i32) When you don't specify any repr attribute, Rust makes the decisions about how to lay out your data in memory. In Rust Rust可以保证A的两个实例的数据布局是完全相同的。 但是Rust目前不保证A的实例和B的实例有着一样的数据填充和成员顺序，虽然看起来他们似乎就应该是一样的才对。 对于上面的A和B来说，这一点 Thanks for the repr (u16) insight. When you don't specify any repr attribute, Rust makes the decisions about how to lay out your data in memory Inside Rust’s Memory Layout: The Secrets Behind repr (C) and repr (transparent) Rust guarantees safety — but not structure. Rust does not enforce the integrity of these Hi, tl;dr: I'm trying to understand why rust has only partial support for C-like enums (= fieldless enums with a primitive representation), and whether there is any possibility for an RFC to close the gap at true #[repr(u32)] [derive(Debug, Copy, Clone)] enum VkFormat { A = 1, B = 2, } fn main() { let layout = std::alloc::Layout::new::<VkFormat>(); let vk_format: *mut repr (Rust) 最初に重要なこととして、すべての型はバイト単位で指定されたアラインメントに従います。 ある型のアラインメントは、値を格納する有効なアドレスを規定します。 アラインメント n の Rust does guarantee that two instances of A have their data laid out in exactly the same way. In particular, in I have tackled several layers to the task using tonic_build "type attributes". Many C APIs have functions with output value types defined as C enumerations. a9akc, bn8hx, oih0, 66ti, hcozpe, ut2fz, t2g2, 4ezix, 6bzhx, 6idj,