generics

问题 I have this program: object B{ def apply[T](c:T)={} } object C{ type T def apply(c:T)={} } object A extends App{ val d=B{println(1);2} val e=C{println(1);2} } the line val e = C{println(1);2} told me error:Type mismatch,expected C.T,actual:2 so why can't I write type T def apply(c:T) it seems the same as apply[T](c:T) and what's the type of T when I write val d=B{println(1);2} I can write many lines here! because T means generic,so it can be Int,String,user defined class Apple,Orange... and

问题 I am trying to enforce a rule that the (dependent) return type of a typeclass, must itself implement a typeclass. So when the user implements the IsVec typeclass below, they must also ensure that the return value of the getElem method implements another typeclass ( IsVecElem ). My attempts to make this work look something like this: // A typeclass for an vector element abstract class IsVecElem[A, T: Numeric] { def dataOnly(self: A): T } // A typeclass for a vector abstract class IsVec[A, T:

问题 I am trying to enforce a rule that the (dependent) return type of a typeclass, must itself implement a typeclass. So when the user implements the IsVec typeclass below, they must also ensure that the return value of the getElem method implements another typeclass ( IsVecElem ). My attempts to make this work look something like this: // A typeclass for an vector element abstract class IsVecElem[A, T: Numeric] { def dataOnly(self: A): T } // A typeclass for a vector abstract class IsVec[A, T:

问题 There are lots of posts on this topic, but all of them are not for a complete beginners in C programming. The thing is that I have three functions: struct model* createModel_empty(void); struct model* createModel_single_value(double value); struct model* createModel_single_value(const double* arr_value); And I want to just use createModel function in my code which will be substituted with the right implementation. From my research over the Internet and specifically stack overflow I understood

问题 There are lots of posts on this topic, but all of them are not for a complete beginners in C programming. The thing is that I have three functions: struct model* createModel_empty(void); struct model* createModel_single_value(double value); struct model* createModel_single_value(const double* arr_value); And I want to just use createModel function in my code which will be substituted with the right implementation. From my research over the Internet and specifically stack overflow I understood

问题 I'm trying to write a function that processes a sequence of integers. fn process_one(n: u32) {} fn process<II>(ii: II) where II: IntoIterator<Item = u32>, { for n in ii { process_one(n); } } I want the client to be able to pass a Vec<u32> without consuming it ( process(&v) ). This function can't be used because <&Vec<u32> as IntoIterator>::Item is &u32 ; I'd have to pass v.iter().cloned() instead, which is annoying. Alternatively, I could make the bound Item = &u32 and use process_one(*n) ,

问题 I'm trying to write a function that processes a sequence of integers. fn process_one(n: u32) {} fn process<II>(ii: II) where II: IntoIterator<Item = u32>, { for n in ii { process_one(n); } } I want the client to be able to pass a Vec<u32> without consuming it ( process(&v) ). This function can't be used because <&Vec<u32> as IntoIterator>::Item is &u32 ; I'd have to pass v.iter().cloned() instead, which is annoying. Alternatively, I could make the bound Item = &u32 and use process_one(*n) ,

问题 I'm trying to write a function that processes a sequence of integers. fn process_one(n: u32) {} fn process<II>(ii: II) where II: IntoIterator<Item = u32>, { for n in ii { process_one(n); } } I want the client to be able to pass a Vec<u32> without consuming it ( process(&v) ). This function can't be used because <&Vec<u32> as IntoIterator>::Item is &u32 ; I'd have to pass v.iter().cloned() instead, which is annoying. Alternatively, I could make the bound Item = &u32 and use process_one(*n) ,

问题 I'm trying to write a function that processes a sequence of integers. fn process_one(n: u32) {} fn process<II>(ii: II) where II: IntoIterator<Item = u32>, { for n in ii { process_one(n); } } I want the client to be able to pass a Vec<u32> without consuming it ( process(&v) ). This function can't be used because <&Vec<u32> as IntoIterator>::Item is &u32 ; I'd have to pass v.iter().cloned() instead, which is annoying. Alternatively, I could make the bound Item = &u32 and use process_one(*n) ,

问题 I'm trying to make a generic struct that can be initialized to something of type T . It looks like this: pub struct MyStruct<T> { test_field: Option<T>, name: String, age: i32, } impl MyStruct<T> { fn new(new_age: i32, new_name: String) -> MyStruct<T> { MyStruct<T> { test_field: None, age: new_age, name: new_name, } } } This doesn't seem to work. Among other errors, I get: error: chained comparison operators require parentheses --> src/lib.rs:9:17 | 9 | MyStruct<T> { | ^^^^^ | 回答1: I highly