generics

问题 I believe my understanding on this is correct but I'd like to check. When creating typeclasses, it feels neater to have them take a single type parameter, like TypeClass[A] . If the typeclass needs to be parameterized in other ways, abstract types can be used, and there is a comparison of the two approaches here: Abstract types versus type parameters So far as I have been able to figure out, one thing which is not mentioned in the link is that if using a type parameter, you can witness that

问题 I believe my understanding on this is correct but I'd like to check. When creating typeclasses, it feels neater to have them take a single type parameter, like TypeClass[A] . If the typeclass needs to be parameterized in other ways, abstract types can be used, and there is a comparison of the two approaches here: Abstract types versus type parameters So far as I have been able to figure out, one thing which is not mentioned in the link is that if using a type parameter, you can witness that

问题 I'm trying to use Expression.NotEqual() (here) But I can't understand how to use the methodInfo. I'm trying to make a comparition to a possible bool?. This is the property that I want to evaluate, wich was added to database after release (creating null's as well as true and falses: public bool? Deactivated { get; set; } = false; I'm using a working expression builder with generic that accepts parameters sent in a object that has a List of WhereParameters like bellow: List<WhereParameters>

问题 I'm trying to use Expression.NotEqual() (here) But I can't understand how to use the methodInfo. I'm trying to make a comparition to a possible bool?. This is the property that I want to evaluate, wich was added to database after release (creating null's as well as true and falses: public bool? Deactivated { get; set; } = false; I'm using a working expression builder with generic that accepts parameters sent in a object that has a List of WhereParameters like bellow: List<WhereParameters>

问题 I'm trying to use Expression.NotEqual() (here) But I can't understand how to use the methodInfo. I'm trying to make a comparition to a possible bool?. This is the property that I want to evaluate, wich was added to database after release (creating null's as well as true and falses: public bool? Deactivated { get; set; } = false; I'm using a working expression builder with generic that accepts parameters sent in a object that has a List of WhereParameters like bellow: List<WhereParameters>

问题 I'm trying to use Expression.NotEqual() (here) But I can't understand how to use the methodInfo. I'm trying to make a comparition to a possible bool?. This is the property that I want to evaluate, wich was added to database after release (creating null's as well as true and falses: public bool? Deactivated { get; set; } = false; I'm using a working expression builder with generic that accepts parameters sent in a object that has a List of WhereParameters like bellow: List<WhereParameters>

问题 How can I restrict the keys of an object to only those that return a certain type? In the example below I want to ensure that the type of the property is a function, so that I can execute obj[key]() . interface IObj{ p1:string, p2:number, p3:()=>void } const obj:IObj = { p1:'str', p2:5, p3:()=>void 0 } function fun<TKey extends keyof IObj>(key: IObj[TKey] extends ()=>void? TKey:never){ const p = obj[key] p(); // This expression is not callable. // Not all constituents of type 'string | number

问题 In the following example, I can't think of any situation where assigning Pick<Object, Key> to Partial<Object> would not be sound, therefore I would expect this to be allowed. Can anyone clarify why it is not allowed? const fn = <T, K extends keyof T>(partial: Partial<T>, picked: Pick<T, K>) => { /* Type 'Pick<T, K>' is not assignable to type 'Partial<T>'. Type 'keyof T' is not assignable to type 'K'. 'keyof T' is assignable to the constraint of type 'K', but 'K' could be instantiated with a

问题 I am trying to write a function to sum an array of numeric types. This is as far as I got: protocol Numeric { } extension Float: Numeric {} extension Double: Numeric {} extension Int: Numeric {} func sum<T: Numeric >(array:Array<T>) -> T{ var acc = 0.0 for t:T in array{ acc = acc + t } return acc } But I don't know how to define the behaviour of the + operator in the Numeric protocol. 回答1: protocol Numeric { func +(lhs: Self, rhs: Self) -> Self } should be enough. Source: http://natecook.com

问题 Im having trouble inheriting an interface containing a method/fun of a base type, that i would like to override as a subtype in the class implementing it. So far i have the interface interface IModel { fun convert(dataModel: BaseDataModel) } And the class implementing it: class SettingsModel: IModel { override fun convert(dataModel: BaseDataModel) { // Conversion of models here } } And i also have the SettingsDataModel which is: class SettingsDataModel: BaseDataModel() { } What i'm trying to