Rust Unconstrained Generic Constant, Appreciate if someone can get a

Rust Unconstrained Generic Constant, Appreciate if someone can get a good workaround for this. Const generic unconstrained generic constant Asked 1 year, 2 months ago Modified 1 year, 2 months ago Viewed 79 times What Are Const Generics? Const generic parameters are a new (ish) kind of generic parameter in Rust, similar to type parameters (e. self. The const identifier introduces a name for the constant parameter, and all instances of the item must be instantiated with a value of Motivation Rust currently has one type which is parametric over constants: the built-in array type [T; LEN]. construct() } } And this is where problem occurs. In fact, there has I'm hitting "generic parameters may not be used in const operations" and "can't use generic parameters from outer item" way too often lately. ilog2(). And Const generic parameters allow items to be generic over constant values. It is written the same as a constant item. I would like to be able to use (but not have to name) a const generic in a generic type, such as: struct Generic<T> (::core::marker::PhantomData<T>); trait NameConst<const N: usize> {} I tried this code: #! [feature (generic_const_exprs)] const B: u8 = 1; const BU: usize = B as usize; fn works<const A: u8> () where [ (); A as usize + BU]:, { (). unit_mul(UR) }>: ，如果去掉这个where，则会报错unconstrained generic constant。 虽然现在还不懂是什么意思. About const expressions in types or why we don't need This post is intended as a continuation of this and earlier discussions between me and @oli-obk. An associated constant definition defines a constant associated with a type. Adding bound with By understanding these principles and applying the appropriate solutions, you'll be well-equipped to tackle the "constrained type is unconstrained" error in your Rust code! Const generic parameters allow items to be generic over constant values. The const identifier introduces a name in the value namespace for the constant parameter, and all instances of the item must be Const generics are generic arguments that range over constant values, rather than types or lifetimes. This allows, for instance, types to be parameterized by integers. Compiler says that Self::Size::N is an unconstrained generic constant, and tries to help with this: try adding a 'where' bound using this Hi, I tried the nightly feature using generic const expressions, but I get the following error message. It will certainly help the expressiveness of the language when it comes to implementing generic My proposal is that #[usable_in_const_generic] will exactly match const generics' restrictions, everything you can do with const generics, but no more, you can also do with . When I add the where clause also to the function "g" it works fine. In fact, there has I had a struct containing a array of values struct WithConstGeneric<const R:usize, T> { values: [T; R] } And I thought it would be nice to use an associated constant instead The type is the type that the definition has to implement. t::< { A as usize }, BU> (); } fn doesnt<const Unconstrained generic constant when using const function to compute generic constant In my journey to type-level programming, I am encountering a rather odd error, unconstrained generic constant that I As a background, what I want to achieve is to get a const/static array with different types and lens given a generic parameter. In generic_function_unconstrained, we take P::Input as an argument, so the caller is 1 当这个奇怪的错误出现时，我正在尝试使用 const 泛型： error: unconstrained generic constant. Associated constant Let's hope that generic constant expressions will find their way in future safe and stable Rust. 这是什么意思？ 也许我应该描述一下在实际代码之前我试图做什么——我想将类型视为数 S { arr } } } Note: this uses an unstable feature (generic_const_exprs) and you need to use the nightly compiler for this you can not define a custom error message (mismatched Rust's const generics allow using constant values as generic parameters, enabling flexibility and performance. g. In the same Your explanation about why I must put any random constraint implying the const generic parameter is really clear, thanks! It does not make really sense IMHO, since if I attempt to use a Unconstrained generic constant when using const function to compute generic constant In my journey to type-level programming, I am encountering a rather odd error, unconstrained generic constant that I Associated constants error: unconstrained generic constant #96595 Closed byte-sourcerer opened this issue on Apr 30, 2022 · 0 comments byte-sourcerer commented on Apr 30, What exactly does "where [ (); Self::LEN]:" mean? Rust needs const wf (well-formedness), and that's the syntax to express it. There are equivalent shorthands for many cases, but the overall requirement is that the constraints are fully specified. You can click the HackMd link in my first reply. I will try to summarize points, } In generic_function_constrained, we explicitly state that the Input associated type must be String. Operations on const-generic How to avoid "unconstrained generic constant" with dependent associated constants in traits? Asked 2 years, 11 months ago Modified 2 years, 11 months ago Viewed 565 times I would like to be able to use (but not have to name) a const generic in a generic type, such as: struct Generic<T> (::core::marker::PhantomData<T>); trait NameConst<const N: usize> {} 这儿对泛型的约束很神奇，竟然是这样写 Quantity<{ UL. However, because const generics are not a first class feature, users cannot I would like to define a struct like this, but the compiler yields an error: #![feature(generic_const_exprs)] struct ArInt&lt;const W: usize, const S: bool&gt; { iarr: [i32; { (W + 31 Const Generics Const generics are generic arguments that range over constant values, rather than types or lifetimes. The way I think about it as Rust user is that for every instantiation of the generic function, all constants are copy-pasted into the function and effectively no "environment" exists since these Suggestion is incorrect: it suggests to add bound on generic constant C, but in the scope where it is used there is no such constant, only Record::S. My primary use case is parametrizing a For now, it looks like you can only directly name const-generic parameters, and have expressions that don't depend on const-generic parameters. They're useful for creating Based on the example in #90455, which after the changes in #90529 would output an unconstrained generic constant error. T) and lifetime parameters (e. The following code, however, does not output Const Generics Const generics are generic arguments that range over constant values, rather than types or lifetimes. 'a). 0. 6xisi6, zs3y, e444n, nngv, szlo, g1l4p, nwqup, v34y, z95j, yyxvd,