TL;DR: What is reified good for fun <T> myGenericFun(c: Class<T>) In the body of a generic function like myGenericFun, you can’t access the type T because it’s only available at compile time but erased at runtime. Therefore, if you want to use the generic type as a normal class in the function body you need … Read more
You need higher-ranked trait bounds (HRTBs), which are described in the advanced Rust book Rustonomicon and well as on Stack Overflow. They allow a type constraint to say that trait must be implemented not just for references with a particular lifetime but for any lifetime. They use the where for<> syntax. Here is the function … Read more
You have a good point of view on this issue here: The Purpose of Scala’s Type System A Conversation with Martin Odersky, Part III by Bill Venners and Frank Sommers (May 18, 2009) Update (October2009): what follows below has actually been illustrated in this new article by Bill Venners: Abstract Type Members versus Generic Type … Read more
Many things are going wrong here: As Shepmaster says, 0 and 1 cannot be converted to everything implementing Integer. Use Zero::zero and One::one instead. 10 can definitely not be converted to anything implementing Integer, you need to use NumCast for that a /= b is not sugar for a = a / b but an … Read more
How to write a trait bound for adding two references of a generic type? Let’s start with a simplified example: fn add_things<T>(a: &T, b: &T) { a + b; } This has the error error[E0369]: binary operation `+` cannot be applied to type `&T` –> src/lib.rs:2:5 | 2 | a + b; | ^^^^^ | … Read more
Generically, a covariant type parameter is one which is allowed to vary down as the class is subtyped (alternatively, vary with subtyping, hence the “co-” prefix). More concretely: trait List[+A] List[Int] is a subtype of List[AnyVal] because Int is a subtype of AnyVal. This means that you may provide an instance of List[Int] when a … Read more
Let’s break down your example a bit: fn cube<T: Mul>(x: T) -> T { let a = x * x; let b = a * x; b } What are the types of a and b? In this case, the type of a is <T as std::ops::Mul>::Output — sound familiar from the error message? Then, … Read more
Here’s a reproduction of your error: struct Foo<T> { val: T, } impl<T> Foo<T> { fn new() -> Self { Foo { val: true } } } fn main() {} The problem arises because you tried to lie to the compiler. This code: impl<T> Foo<T> { fn new() -> Self { /* … */ } … Read more