enums

问题 I am storing enums for things such as ranks (administrator, moderator, user...) and achievements for each user in my Mongo database. As far as I know Mongo does not have an enum data type which means I have to store it using another type. I have thought of storing it using integers which I would assume uses less space than storing strings for everything that could easily be expressed as an integer. Another upside I see of using integers is that if I wanted to rename an achievement or rank I

问题 I am storing enums for things such as ranks (administrator, moderator, user...) and achievements for each user in my Mongo database. As far as I know Mongo does not have an enum data type which means I have to store it using another type. I have thought of storing it using integers which I would assume uses less space than storing strings for everything that could easily be expressed as an integer. Another upside I see of using integers is that if I wanted to rename an achievement or rank I

问题 Say I have the below enum [Flags] enum Letters { A = 1, B = 2, C = 4, D = 8, E = 16, F = 32, AB = A | B, All = A | B | C, } If I have the variables: var s = Letters.A | Letters.B | Letters.D; var p = Letters.A | Letters.C | Letters.D | Letters.E; What I want is to get the common values between these two enums so in this case it should be A | D . Can some one please tell me how I can achieve this. Thanks 回答1: You can get that using the binary & (and) operator: var s = Letters.A | Letters.B |

问题 Is there a simple way to convert an integer value to enum? I want to retrieve an integer value from shared preference and convert it to an enum type. My enum is: enum ThemeColor { red, gree, blue, orange, pink, white, black }; I want to easily convert an integer to an enum: final prefs = await SharedPreferences.getInstance(); ThemeColor c = ThemeColor.convert(prefs.getInt('theme_color')); // something like that 回答1: int idx = 2; print(ThemeColor.values[idx]); should give you ThemeColor.blue

问题 I saw answers like these, tried to clarify via comments, and was unsatisfied by examples here. Maybe it's time for this specific question... Why enum singleton implementation is called lazy ? public enum EnumLazySingleton { INSTANCE; EnumLazySingleton() { System.out.println("constructing: " + this); } public static void touchClass() {} } How it is different from eager implementation? public class BasicEagerSingleton { private static final BasicEagerSingleton instance = new BasicEagerSingleton

问题 I saw answers like these, tried to clarify via comments, and was unsatisfied by examples here. Maybe it's time for this specific question... Why enum singleton implementation is called lazy ? public enum EnumLazySingleton { INSTANCE; EnumLazySingleton() { System.out.println("constructing: " + this); } public static void touchClass() {} } How it is different from eager implementation? public class BasicEagerSingleton { private static final BasicEagerSingleton instance = new BasicEagerSingleton

问题 I'm trying to achieve an OpenAPI definition where I define a shared, complete list of allowed values as an enum and then use subgroups of the values in different places to show which values are allowed in each case. Using the example from the enum spec on Swagger.io, if I have a definition like this: paths: /products: get: parameters: - in: query name: color required: true schema: $ref: '#/components/schemas/Color' responses: '200': description: OK components: schemas: Color: type: string

问题 I'm trying to achieve an OpenAPI definition where I define a shared, complete list of allowed values as an enum and then use subgroups of the values in different places to show which values are allowed in each case. Using the example from the enum spec on Swagger.io, if I have a definition like this: paths: /products: get: parameters: - in: query name: color required: true schema: $ref: '#/components/schemas/Color' responses: '200': description: OK components: schemas: Color: type: string

问题 When one already knows all the finite number of types involved in some code which needs dynamic polymorphism, using enum can be better for performances compared to using Box since the latter uses dynamic memory allocation and you'll need to use trait objects which have virtual function call as well. That said, compared to the equivalent code in C++ using std::variant and std::visit , looks like Rust in this scenario has more boilerplate coding involved, at least for me (I have not yet learned

问题 When one already knows all the finite number of types involved in some code which needs dynamic polymorphism, using enum can be better for performances compared to using Box since the latter uses dynamic memory allocation and you'll need to use trait objects which have virtual function call as well. That said, compared to the equivalent code in C++ using std::variant and std::visit , looks like Rust in this scenario has more boilerplate coding involved, at least for me (I have not yet learned