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What is default value of KeyValuePair<string, int>?
e.g. I am running a LINQ query and returning FirstOrDefault() value from it
KeyValuePair<string, int> mapping = (from p in lstMappings where p.Key.Equals(dc.ColumnName, StringComparison.InvariantCultureIgnoreCase) select p).FirstOrDefault(); if (mapping != null) { } how to check if mapping object is null/blank
(I am getting compile time error in above code Operator '!=' cannot be applied to operands of type 'System.Collections.Generic.KeyValuePair<string,int>' and '<null>')
PS: lstMappings is of type
List<KeyValuePair<string, int>> 
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default equals to null. And default(KeyValuePair<T,U>) is an actual KeyValuePair that contains null, null .
The KeyValuePair class stores a pair of values in a single list with C#. Set KeyValuePair and add elements − var myList = new List<KeyValuePair<string, int>>(); // adding elements myList. Add(new KeyValuePair<string, int>("Laptop", 20)); myList.
KeyValuePair is immutable - it's also a value type, so changing the value of the Value property after creating a copy wouldn't help anyway.
You can't modify it, you can replace it with a new one.
The default value of any type T is default(T), so for 100% theoretical accuracy you would write
if (!mapping.Equals(default(KeyValuePair<string, int>))) { // ... } Since KeyValuePair is a struct (i.e. a value type) you cannot compare it to null. Irrespective of that, comparing values with == is wrong as a default approach because if used on reference types it normally checks for reference equality.
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