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QuestionWCF UnobservedTaskException Pin
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Question'Switch on 'Type: C# 7,8 offer no relief; and, Eric Lippert is still right Pin
BillWoodruff18-Jul-19 4:15
mveBillWoodruff18-Jul-19 4:15 
A long time ago, Eric wrote:
Quote:
Any time you find yourself switching on a type in a generic you are almost certainly doing something wrong. Generics should be generic; they should operate identically completely independent of the type.

If T can only be int or string then don't write your code this way at all in the first place. Write two methods, one that returns an int and one that returns a string.
Of course, Eric is always right !

I thought the new pattern-matching facilities in C# 7,8 might allow me to simplify a 'Switch based on a Generic Type; here's a compilable (VS 2019, FrameWork 4.8) example:
// 'KeyType has been set in the class initializer

public TKey GetNextKey(TKey key = default(TKey))
{
    if (! KeysUsed.Contains(key))
    {
        CurrentKey = key;
        KeysUsed.Add(key);
        return key;
    }
    
    switch (KeyType)
    {
        case Type _ when KeyType == typeof(Int32):
            int i = (Int32) (object) key + 1;
            CurrentKey = (TKey)(object) i;
            break;
        case Type _ when KeyType == typeof(string):  // incomplete
            string s = (string) (object) key;
            s += GetAGuid(); // code not shown here
            CurrentKey = (TKey)(object)s;
            break;

        default:
            throw new ArgumentException("unsupported TKey Type");
    }

    KeysUsed.Add(CurrentKey);
    return CurrentKey;
}
Okay, if you think "case Type _ when KeyType == typeof(Int32):" is simplification ... game over.

What really irritates me is the conversions to object necessary here. This issue came up in a QA question here in 2016; see FES_SiteCore's solution: [^]

references: Mads Torgensen on C# 8 patterns: [^], ReSharper recent blog: [^]
«Where is the Life we have lost in living? Where is the wisdom we have lost in knowledge? Where is the knowledge we have lost in information?» T. S. Elliot


modified 18-Jul-19 10:32am.

SuggestionRe: 'Switch on 'Type: C# 7,8 offer no relief; and, Eric Lippert is still right Pin
Richard Deeming18-Jul-19 5:02
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GeneralRe: 'Switch on 'Type: C# 7,8 offer no relief; and, Eric Lippert is still right Pin
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GeneralRe: 'Switch on 'Type: C# 7,8 offer no relief; and, Eric Lippert is still right Pin
honey the codewitch20-Jul-19 10:47
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GeneralRe: 'Switch on 'Type: C# 7,8 offer no relief; and, Eric Lippert is still right Pin
BillWoodruff20-Jul-19 13:34
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GeneralRe: 'Switch on 'Type: C# 7,8 offer no relief; and, Eric Lippert is still right Pin
honey the codewitch20-Jul-19 13:38
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QuestionProblem deserialising JSON data [SOLVED by the brilliant Richard Deeming] Pin
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QuestionGetting Exception Window Class Name is not Valid in Windows Application using vb.net Pin
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