C# 4: What's the Difference Between `dynamic` and `var` Keywords?

C# 4: Understanding the Differences Between dynamic and var

This article clarifies the key distinctions between the dynamic and var keywords in C# 4, crucial for writing efficient and robust code.

var: Streamlining Static Typing

The var keyword, introduced in C# 4, simplifies variable declarations by allowing type inference. The compiler automatically determines the variable's type based on its initialization value. For example:

<code class="language-csharp">var s = "abc";
Console.WriteLine(s.Length);</code>

This is functionally identical to explicitly declaring the string type:

<code class="language-csharp">string s = "abc";
Console.WriteLine(s.Length);</code>

In both cases, the compiler correctly infers s as a string.

dynamic: Leveraging Runtime Flexibility

dynamic, also a C# 4 feature, introduces dynamic typing. Unlike var, it defers type checking until runtime. This is beneficial when working with objects whose properties and methods aren't known at compile time:

<code class="language-csharp">dynamic s = "abc";
Console.WriteLine(s.Length);</code>

Here, s is declared as dynamic. The compiler doesn't verify s.Length exists; this resolution happens during execution. While this offers flexibility, it also introduces the risk of runtime errors if a property or method doesn't exist.

In Summary

var streamlines statically-typed code by reducing redundant type declarations, enhancing readability. dynamic provides runtime flexibility for scenarios involving dynamically-defined objects. The choice depends on whether compile-time type safety or runtime adaptability is prioritized.

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