C#

[C#] VAR keyword

Beginning in Visual C# 3.0, variables that are declared at method scope can have an implicit “type” var. An implicitly typed local variable is strongly typed just as if you had declared the type yourself, but the compiler determines the type.

In some case like below example, var must be used because the result is a collection of anonymous types, and the name of that type is not accessible except to the compiler itself. Note that in Example #2, the foreach iteration variable item must also be implicitly typed.

// Example #1: var is optional because
// the select clause specifies a string
string[] words = { "apple", "strawberry", "grape", "peach", "banana" };
var wordQuery = from word in words
                where word[0] == 'g'
                select word;

// Because each element in the sequence is a string, 
// not an anonymous type, var is optional here also.
foreach (string s in wordQuery)
{
    Console.WriteLine(s);
}

// Example #2: var is required because
// the select clause specifies an anonymous type
var custQuery = from cust in customers
                where cust.City == "Phoenix"
                select new { cust.Name, cust.Phone };

// var must be used because each item 
// in the sequence is an anonymous type
foreach (var item in custQuery)
{
    Console.WriteLine("Name={0}, Phone={1}", item.Name, item.Phone);
}

 

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