How should I cast in VB NET

Question

Are all of these equal   Under what circumstances should I choose each over the others    var ToString   CStr var  CType var  String  DirectCast var  String      EDIT  Suggestion from NotMyself hellip    TryCast var  String

User · Answer

According to the certification exam you should use Convert ToXXX   whenever possible for simple conversions because it optimizes performance better than CXXX conversions

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At one time  I remember seeing the MSDN library state to use CStr   because it was faster  I do not know if this is true though

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User Konrad Rudolph advocates for DirectCast   in Stack Overflow question  Hidden Features of VB NET

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Cstr   is compiled inline for better performance   CType allows for casts between types if a conversion operator is defined  ToString   Between base type and string throws an exception if conversion is not possible   TryParse   From String to base typeif possible otherwise returns false  DirectCast used if the types are related via inheritance or share a common interface   will throw an exception if the cast is not possible  trycast will return nothing in this instance

User · Answer

MSDN seems to indicate that the Cxxx casts for specific types can improve performance in VB  NET because they are converted to inline code   For some reason  it also suggests DirectCast as opposed to CType in certain cases  the documentations states it s when there s an inheritance relationship  I believe this means the sanity of the cast is checked at compile time and optimizations can be applied whereas CType always uses the VB runtime    When I m writing VB  NET code  what I use depends on what I m doing  If it s prototype code I m going to throw away  I use whatever I happen to type   If it s code I m serious about  I try to use a Cxxx cast   If one doesn t exist  I use DirectCast if I have a reasonable belief that there s an inheritance relationship   If it s a situation where I have no idea if the cast should succeed  user input -  integers  for example   then I use TryCast so as to do something more friendly than toss an exception at the user   One thing I can t shake is I tend to use ToString instead of CStr but supposedly Cstr is faster

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I prefer the following syntax   Dim number As Integer   1 Dim str As String   String TryCast number   If str IsNot Nothing Then   Hah you can tell I typically write code in C   8    The reason I prefer TryCast is you do not have to mess with the overhead of casting exceptions  Your cast either succeeds or your variable is initialized to null and you deal with that accordingly

User · Answer

Those are all slightly different  and generally have an acceptable usage    var ToString   is going to give you the string representation of an object  regardless of what type it is   Use this if var is not a string already  CStr var  is the VB string cast operator   I m not a VB guy  so I would suggest avoiding it  but it s not really going to hurt anything   I think it is basically the same as CType  CType var  String  will convert the given type into a string  using any provided conversion operators  DirectCast var  String  is used to up-cast an object into a string   If you know that an object variable is  in fact  a string  use this   This is the same as  string var in C   TryCast  as mentioned by  NotMyself  is like DirectCast  but it will return Nothing if the variable can t be converted into a string  rather than throwing an exception   This is the same as var as string in C    The TryCast page on MSDN has a good comparison  too

[.net] How should I cast in VB.NET?

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