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How to branch code based on class data type


By : Nick Olszowy
Date : August 01 2020, 02:00 AM
Hope that helps I am attempting to implement some more complex data structures in c# working with no libraries other than System. Currently i am working on graphs. , Well you could use pattern matching:
code :
switch (edge)
{
    case directedEdge<dataType> de:
        // Do whatever..
        break;
    case undirectedEdge<dataType> ue:
        // Do whatever..
        break;
    default:
        // Do whatever..
        break;
}
abstract class Edge
{
    abstract void DoSomething();
}

class directedEdge<T> : Edge
{
    override void DoSomething() { }
}

class undirectedEdge<T> : Edge
{
    override void DoSomething() { }
}
Edge edge = // Some specific edge type
edge.DoSomething();


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How can I update the base type's data to a derived class while using EF code first table per type


By : Tom Carwardine
Date : March 29 2020, 07:55 AM
Hope that helps This is a common design mistake.
Objects can't change their type; you shouldn't be using inheritance in this case.

Entity Framework Code First - select based on type of child TPH class


By : Avery Bell
Date : March 29 2020, 07:55 AM
may help you .
Is it possible to find a list of items that share a child table type using Linq To Entities?
code :
public static class Extensions
{
    public static IQueryable<InventoryItem> WhereIsLastState(
        this IQueryable<InventoryItem> query, Type state)
    {
        if (state == typeof(InactiveState))
            return query.Where(i => i.LastState is InactiveState);
        if (state == typeof(ActiveState))
            return query.Where(i => i.LastState is ActiveState);
        if (state == typeof(CompletedState))
            return query.Where(i => i.LastState is CompletedState);

        throw new InvalidOperationException("Unsupported type...");
    }
}
public ICollection<InventoryItem> GetInventoryItemsByState(Type state)
{
   return inventoryRepository.Get().WhereIsLastState(state).ToList();
}
var result = context.InventoryItems
    .Select(i => new
    {
        InventoryItem = i,
        LastState = i.LastState,
        StateStore = (i.LastState is InactiveState)
            ? (i.LastState as InactiveState).StateStore
            : null
    })
    .AsEnumerable()
    .Select(x => x.InventoryItem)
    .ToList();

Why I should specific class B parameters type when defining a parameter type constraint in a class A based on B's type?


By : user2770492
Date : March 29 2020, 07:55 AM
may help you . When you create a generic type, you're creating a conceptual "template" more than a complete type. It can only become a complete type when you specify the missing pieces in the template: the concrete types.
Type constraints are there so the compiler can add some type-checking. Even if you don't know the exact type that's going to be used, if it inherits from a base, you know what base members are available to your code. If you try to constrain a type parameter with a generic type without type arguments, the compiler doesn't have enough information to understand what methods will actually be available.

mapping with an if statement based on data/class type


By : user3673673
Date : March 29 2020, 07:55 AM
I wish did fix the issue. The attrs "class" can extract the "class" and then we do a comparison with if/else
code :
library(xgboost)
library(purrr)
out1 <- map2_dfr(models_list, boundary_lists, ~ {
       mods <- pluck(.x, "models")
       dat <- .y
       map_dfr(mods,  ~if(attr(.x, "class")[1] == "xgb.Booster") {

       tibble(modelname = attr(.x, "class")[1], 
         prediction = predict(.x, newdata = as.matrix(dat), type = 'prob')) 
          } else {
          tibble(modelname = attr(.x, "class")[1],
          prediction = predict(.x, newdata = dat))}   )   

       }, .id = 'grp' 

       )




head(out1)
# A tibble: 6 x 3
#  modelname prediction grp  
#  <chr>          <dbl> <chr>
#1 glm             1.95 1    
#2 glm             1.97 1    
#3 glm             1.98 1    
#4 glm             1.99 1    
#5 glm             2.00 1    
#6 glm             2.01 1    

Relative performance of using C++ Class based and struct based data type


By : Arcadia
Date : March 29 2020, 07:55 AM
this one helps. No. A class is the same exact thing as a struct, the only thing that changes is that, by default, class members are private and struct members are public.
There are also more changes related to inheritance and access type, but for more info on that check this question.
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