When is efficient to use anonymous types?

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I mean "var" keyword.For example

C#

var a=10;

or

C#

int a=10;

.In my opinion program will work worth,becouse in situation of using var keyword,compiler should choose right type for given variable.

Posted 23-Jan-15 5:47am

Inimicos

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DamithSL 23-Jan-15 11:57am

there is no run time performance difference when using var and not using var, can you elaborate more on your question?

Sergey Alexandrovich Kryukov 23-Jan-15 12:12pm

Not only it does not affect performance; it has nothing to do with runtime at all; this is merely syntactic sugar. Please see the comment below and my answer.
—SA

Zoltán Zörgő 23-Jan-15 11:59am

DamithSL is right: var is resolved at compile-time. Even before, as even Visual Studio can figure out what is the type.

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-01-23T06:11:00

This is not an anonymous type; this is just a type obtained from type inference. Consider

C#

var stringBuilder = new System.Text.StringBuilder();
string whatIsIt = stringBuilder.GetType().FullName;

The last line will return "System.Text.StringBuilder", quite fully named :-); and the first line is strictly equivalent to

C#

System.Text.StringBuilder(); stringBuilder = new System.Text.StringBuilder();

So, this is nothing but syntax, syntactic sugar (http://en.wikipedia.org/wiki/Syntactic_sugar[^]).

You can try the same with the number and the string, will see a concrete named type.

I guess it's apparent when you can use this feature: when you know that "compiler's guess" is apparent and you get what you expected.

And anonymous type is something totally different: https://msdn.microsoft.com/en-us/library/bb397696.aspx[^].

—SA