Option Explicit and Option Strict in VB .NET

Generally it is a MUST to put ‘Option Explicit’ and ‘Option Strict’ at the top of all my .net classes.

Option Explicit Statement
By default, the Visual Basic .NET or Visual Basic 2005 compiler enforces explicit variable declaration, which requires that you declare every variable before you use it.

Option Strict Statement
‘Option Strict’ keeps VB developers coding bad casts. By default, the Visual Basic .NET or Visual Basic 2005 compiler does not enforce strict data typing.

In Visual Basic .NET, you can convert any data type to any other data type implicitly. Data loss can occur when the value of one data type is converted to a data type with less precision or with a smaller capacity. However, you receive a run-time error message if data will be lost in such a conversion. Option Strict notifies you of these types of conversions at compile time and restricts implicit type conversions, so that you can avoid them. It also verifies that functions have return types and all paths return a value. it helps to catch lot of possible errors, but it is off by default.

To enable the Option Strict and Option Explicit statements in the code-behind files and files that are contained in the App_Code folder of a Visual Basic application, add the following code to the Web.config file:

<system.codedom>
<compilers>
<compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" warningLevel="0" />
<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" warningLevel="0" />
</compilers>
</system.codedom>