The default for KeyValuePair

Question

I have an object of the type IEnumerable lt KeyValuePair lt T U gt  gt  keyValueList  I am using    var getResult  keyValueList SingleOrDefault     if getResult    default            else          How can I check whether getResult is the default  in case I can t find the correct element   I can t check whether it is null or not  because KeyValuePair is a struct

User · Answer

Try this   KeyValuePair lt string int gt  current   this recent SingleOrDefault r   gt  r Key Equals dialog FileName     true    if  current Key    null      this recent Add new KeyValuePair lt string int gt  dialog FileName 0

User · Answer

I recommend more understanding way using extension method   public static class KeyValuePairExtensions       public static bool IsNull lt T  TU gt  this KeyValuePair lt T  TU gt  pair                return pair Equals new KeyValuePair lt T  TU gt                And then just use   var countries   new Dictionary lt string  string gt          cz    prague          de    berlin       var country   countries FirstOrDefault x   gt  x Key     en     if country IsNull

User · Answer

if getResult Key Equals default T    amp  amp  getResult Value Equals default U

User · Answer

You can create a general  and generic  extension method  like this one   public static class Extensions       public static bool IsDefault lt T gt  this T value  where T   struct               bool isDefault   value Equals default T             return isDefault            Usage      We have to set explicit default value  0  to avoid build error     Use of unassigned local variable  intValue  int intValue   0  long longValue   12  KeyValuePair lt String  int gt  kvp1   new KeyValuePair lt String  int gt   string   11   KeyValuePair lt String  int gt  kvp2   new KeyValuePair lt String  int gt     List lt KeyValuePair lt String  int gt  gt  kvps   new List lt KeyValuePair lt String  int gt  gt    kvp1  kvp2    KeyValuePair lt String  int gt  kvp3   kvps FirstOrDefault kvp   gt  kvp Value    11   KeyValuePair lt String  int gt  kvp4   kvps FirstOrDefault kvp   gt  kvp Value    15    Console WriteLine intValue IsDefault        results  True  Console WriteLine longValue IsDefault        results  False  Console WriteLine kvp1 IsDefault        results  False  Console WriteLine kvp2 IsDefault        results  True  Console WriteLine kvp3 IsDefault        results  False  Console WriteLine kvp4 IsDefault        results  True

User · Answer

From your original code it looks like what you want is to check if the list was empty   var getResult  keyValueList SingleOrDefault    if  keyValueList Count    0          default      else

User · Answer

Try this   if  getResult Equals new KeyValuePair lt T U gt        or this   if  getResult Equals default KeyValuePair lt T U gt

User · Answer

To avoid the boxing of KeyValuePair Equals object  you can use a ValueTuple   if   getResult Key  getResult Value     default

[c#] The default for KeyValuePair

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