I want to create a class with a public enum (to be used by other modules) with an internal String raw value (I don't want other modules to read the raw Value, but I do want to read it internally inside the same module).
I know I can just create another private function that receives the enum and returns a String but I want to avoid that.
I think it's not possible, I tried doing like this first:
public enum Emotion {
case Hate = EmotionInner.Hate, Love = EmotionInner.Love
}
internal enum EmotionInner: String {
case Hate = "hate", Love = "love"
}
But it won't compile.
Your enums at least should be the same type - so if you want to has rawValue() it will has it in both enum. And you can't make rawValue() smth like final or static.
By the way, maybe it's not bad way to make a function for it?
Related
I want to express the extends behavior many languages possess.
In my Go Code I have a few structs that look like so:
type Base struct {
// Some fields
}
type BaseExtender struct {
Base
// Unique fields
}
type AnotherBaseExtender struct {
Base
// Unique fields
}
Now, I want to write a function that takes any Base since I only need it's "similar fields".
func UseTheBase(b Base) {
testVal := b.thingICareAbout
}
However, this doesn't work. I've done some digging into interface and thought I could do something like:
type Base interface {
// Some fields
}
Except it appears that Go automatically infers interfaces by method implementation. Is there a way to mimic this behavior so I can pass any Base into my function, and not have to implement some nop method on the Base struct and all of it's extenders?
Thanks!
Base implies you want inheritance in Go, Go deliberately eschews inheritance, don't try to recreate it. You can embed types but think of this as embedding behaviour, not just data (as you might be tempted to in an inheriting language).
You're on the right lines with your solution but need public methods and yes interfaces are defined in terms of methods. Just define the interface where you call it as:
type Doer interface {
DoSomething()
}
...
func doit(d Doer) {
d.DoSomething()
}
doit doesn't care what its argument is as long as it has a DoSomething method. Obviously this is a trivial example and there's no point in it, but if you need to override something in all extenders, ask yourself why Base exists, if it is just to add some fields, that's probably not enough reason for a separate type, just add the fields where you need them.
Try to avoid the vast taxonomies of types that you might construct in other languages.
To add on, a common pattern I use is:
type Base interface {
SomeFunction() int
}
type SimpleBaseImpl struct {
// Unique fields
}
func (s SimpleBaseImpl) SomeFunction() int {
return 0
}
type SomethingMoreComplicated struct {
SimpleBaseImpl
// Unique fields
}
Then you could treat SomethingMoreComplicated as "type" Base – but again, its important to note the golang preference for composition (shown here) over inheritance.
TypeScript's type system uses type annotations, which look like this:
private currentState: IAppState;
I read this as "currentState is an IAppState"
Why does this syntax make more design sense than this, which is what I'm used to from other strongly-typed languages?
private IAppState currentState;
I understand that TypeScript is supposed to be an extension of JavaScript syntax, but in that case, what made the designers of TypeScript choose the current syntax over this:
private IAppState: currentState;
A friend and I were discussing it and he raised a good example:
type student_detail = {
id: number,
name: string,
percentage: number,
clg_data: {
college_id: number,
college_name: string
}
}
This almost looks like standard JS. Now imagine what you'd have with C style syntax:
struct student_detail {
number id;
string name;
number percentage;
// structure within structure
struct {
number college_id;
string college_name;
} clg_data;
}
When it comes to structures in structures the only way to really do it is by splitting them out into separate structures:
struct student_college_detail {
number college_id;
string college_name;
};
struct student_detail {
number id;
string name;
number percentage;
struct student_college_detail clg_data;
}
This is fine but doesn't really fit into JavaScript. This is likely the reason why they stuck with the var: type syntax. It would maybe be nice if you could do either though. :)
Is there a way to use enum default parameters in Haxe? I get this error:
Parameter default value should be constant
enum AnEnum {
A;
B;
C;
}
class Test {
static function main() {
Test.enumNotWorking();
}
static function enumNotWorking(e:AnEnum = AnEnum.A){}
}
Try Haxe link.
Update: this feature has been added in Haxe 4. The code example from the question now compiles as-is with a regular enum.
Previously, this was only possible if you're willing to use enum abstracts (enums at compile time, but a different type at runtime):
#:enum
abstract AnEnum(Int)
{
var A = 1;
var B = 2;
var C = 3;
}
class Test3
{
static function main()
{
nowItWorks();
}
static function nowItWorks(param = AnEnum.A)
{
trace(param);
}
}
There's nothing special about the values I chose, and you could choose another type (string, or a more complex type) if it better suits your use case. You can treat these just like regular enums (for switch statements, etc.) but note that when you trace it at runtime, you'll get "1", not "A".
More information: http://haxe.org/manual/types-abstract-enum.html
Sadly enums can't be used as default values, because in Haxe enums aren't always constant.
This piece of trivia was on the old website but apparently hasn't made it into the new manual yet:
http://old.haxe.org/ref/enums#using-enums-as-default-value-for-parameters
The workaround is to check for a null value at the start of your function:
static function enumNotWorking(?e:AnEnum){
if (e==null) e=AnEnum.A;
}
Alternatively, an Enum Abstract might work for your case.
I was reading a book about Linq, and saw that the Distinct method has an overload that takes a comparer. This would be a good solution to a problem I have where I want to get the distinct entities from a collection, but want the comparison to be on the entity ID, even if the other properties are different.
According to the book, if I have a Gribulator entity, I should be able to create a comparer like this...
private class GribulatorComparer : IComparer<Gribulator> {
public int Compare(Gribulator g1, Gribulator g2) {
return g1.ID.CompareTo(g2.ID);
}
}
...and then use it like this...
List<Gribulator> distinctGribulators
= myGribulators.Distinct(new GribulatorComparer()).ToList();
However, this gives the following compiler errors...
'System.Collections.Generic.List' does not contain a definition for 'Distinct' and the best extension method overload 'System.Linq.Enumerable.Distinct(System.Collections.Generic.IEnumerable, System.Collections.Generic.IEqualityComparer)' has some invalid arguments
Argument 2: cannot convert from 'LinqPlayground.Program.GribulatorComparer' to 'System.Collections.Generic.IEqualityComparer'
I've searched around a bit, and have seen plenty of examples that use code like this, but no complaints about compiler errors.
What am I doing wrong? Also, is this the best way of doing this? I want a one-off solution here, so don't want to start changing the code for the entity itself. I want the entity to remain as normal, but just in this one place, compare by ID only.
Thanks for any help.
You're implementing your comparer as an IComparer<T>, the LINQ method overload requires an implementation of IEqualityComparer:
private class GribulatorComparer : IEqualityComparer<Gribulator> {
public bool Equals(Gribulator g1, Gribulator g2) {
return g1.ID == g2.ID;
}
}
edit:
For clarification, the IComparer interface can be used for sorting, as that's basically what the Compare() method does.
Like this:
items.OrderBy(x => new ItemComparer());
private class ItemComparer : IComparer<Item>
{
public int Compare(Item x, Item y)
{
return x.Id.CompareTo(y.Id)
}
}
Which will sort your collection using that comparer, however LINQ provides a way to do that for simple fields (like an int Id).
items.OrderBy(x => x.Id);
Here's my problem. A class which defines an order has a property called PaymentStatus, which is an enum defined like so:
public enum PaymentStatuses : int
{
OnDelivery = 1,
Paid = 2,
Processed = 3,
Cleared = 4
}
And later on, in the class itself, the property definition is very simple:
public PaymentStatuses? PaymentStatus { get; set; }
However, if I try to save an order to the Azure Table Storage, I get the following exception:
System.InvalidOperationException: The type Order+PaymentStatuses' has no settable properties.
At this point I thought using enum isn't possible, but a quick Google search returned this: http://social.msdn.microsoft.com/Forums/en-US/windowsazure/thread/7eb1a2ca-6c1b-4440-b40e-012db98ccb0a
This page lists two answers, one of which seems to ignore the problems and suggests that using an enum in Azure Storage is fine.
Now, I don't NEED to store the enum in the Azure Table Storage as such, I could just as well store a corresponding int, however, I do need this property to be exposed in the WCF service.
I've tried making the property use get and set to return the enum from a stored integer, and remove this property from Azure by using the WritingEntity event on my DataContext, but I get that exception before the event for this entity is fired.
At this point, I'm at a loss, I don't know what else I can do to have this property in WCF as an enum, but have Azure store just the int.
Enum is not supported. Even though it is defined like an int, it is really not an integral type supported by Table Storage. Here is the list of types supported. An enum is just a string expression of an integral number with an object-oriented flavor.
You can store int in table storage and then convert it using Enum.Parse.
Here's a simple workaround:
public int MyEnumValue { get; set; } //for use by the Azure client libraries only
[IgnoreProperty] public MyEnum MyEnum
{
get { return (MyEnum) MyEnumValue; }
set { MyEnumValue = (int) value; }
}
It would have been nicer if a simple backing value could have been employed rather than an additional (public!) property - without the hassle of overriding ReadEntity/WriteEntity of course. I opened a user voice ticket that would facilitate that, so you might want to upvote it.
ya i was having this same problem
i changed my property which was earlier enum to int. now this int property parses the incoming int and saves it into a variale of the same enum type so now the code that was
public CompilerOutputTypes Type
{get; set;}
is chaged to
private CompilerOutputTypes type;
public int Type
{
get {return (int)type;}
set { type = (CompilerOutputTypes)value; }
}
Just suggestions...
I remember that in WCF you have to mark enums with special attributes: http://msdn.microsoft.com/en-us/library/aa347875.aspx
Also, when you declare PaymentStatuses? PaymentStatus, you are declaring Nullable<PaymentStatuses> PaymentStatus. The ? sintax is just syntactic sugar. Try to remove the ? and see what happen (you could add a PaymentStatuses.NoSet = 0 , because the default value for an Int32 is 0).
Good luck.
Parvs solution put me on the right track but I had some minor adjustments.
private string _EnumType;
private EnumType _Type;
//*********************************************
//*********************************************
public string EnumType
{
get { return _Type.ToString(); }
set
{
_EnumType = value;
try
{
_Type = (EnumType)Enum.Parse(typeof(EnumType), value);
}
catch (Exception)
{
_EnumType = "Undefined";
_Type = [mynamespace].EnumType.Undefined;
}
}
}
I have come across a similar problem and have implemented a generic object flattener/recomposer API that will flatten your complex entities into flat EntityProperty dictionaries and make them writeable to Table Storage, in the form of DynamicTableEntity.
Same API will then recompose the entire complex object back from the EntityProperty dictionary of the DynamicTableEntity.
This is relevant to your question because the ObjectFlattenerRecomposer API supports flattening property types that are normally not writeable to Azure Table Storage like Enum, TimeSpan, all Nullable types, ulong and uint by converting them into writeable EntityProperties.
The API also handles the conversion back to the original complex object from the flattened EntityProperty Dictionary. All that the client needs to do is to tell the API, I have this EntityProperty Dictionary that I just read from Azure Table (in the form of DynamicTableEntity.Properties), can you convert it to an object of this specific type. The API will recompose the full complex object with all of its properties including 'Enum' properties with their original correct values.
All of this flattening and recomposing of the original object is done transparently to the client (user of the API). Client does not need to provide any schema or any knowledge to the ObjectFlattenerRecomposer API about the complex object that it wants to write, it just passes the object to the API as 'object' to flatten it. When converting it back, the client only needs to provide the actual type of object it wants the flattened EntityProperty Dictionary to be converted to. The generic ConvertBack method of the API will simply recompose the original object of Type T and return it to the client.
See the usage example below. The objects do not need to implement any interface like 'ITableEntity' or inherit from a particular base class either. They do not need to provide a special set of constructors.
Blog: https://doguarslan.wordpress.com/2016/02/03/writing-complex-objects-to-azure-table-storage/
Nuget Package: https://www.nuget.org/packages/ObjectFlattenerRecomposer/
Usage:
//Flatten object (ie. of type Order) and convert it to EntityProperty Dictionary
Dictionary<string, EntityProperty> flattenedProperties = EntityPropertyConverter.Flatten(order);
// Create a DynamicTableEntity and set its PK and RK
DynamicTableEntity dynamicTableEntity = new DynamicTableEntity(partitionKey, rowKey);
dynamicTableEntity.Properties = flattenedProperties;
// Write the DynamicTableEntity to Azure Table Storage using client SDK
//Read the entity back from AzureTableStorage as DynamicTableEntity using the same PK and RK
DynamicTableEntity entity = [Read from Azure using the PK and RK];
//Convert the DynamicTableEntity back to original complex object.
Order order = EntityPropertyConverter.ConvertBack<Order>(entity.Properties);