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[.net] How do you typically cast in VB.NET?


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#1 graveyard filla   Members   -  Reputation: 583

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Posted 03 January 2007 - 12:24 PM

Hi, What is the 'standard' way to cast things in VB.NET? I have been using CStr,CDate,CBool, etc, along with CType() where the built in type is not found... However i've recently been informed that the C* functions (except CType) are non-standard and could possibly be removed from the framework one day, although not very likely to ever happen... And now that I think back, I think I only started using the C* functions because of all my experience coming from a C++ background.... What is the way to do a C-style cast then? What about the C-style template castings (like dynamic_cast<>)? Is the former the C* functions, and the latter the Convert.* functions? Should I strictly use the Convert Class for everything, except where DirectCast is appopriate? OR should I stick with my C style casts, or what? I DO understand that you should use DirectCast when you *know* there is a parent/child relationship... but what other rules of thumb should I follow for using what casting styles? Thanks for any help [Edited by - graveyard filla on January 3, 2007 6:48:36 PM]

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#2 daviangel   Members   -  Reputation: 600

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Posted 03 January 2007 - 07:47 PM

Personally I use DirectCast when I can in most of my VB code since it's a bit faster.
"
The DirectCast keyword offers yet another way to cast a type to a different type. This keyword has the same syntax as CType but differs from the latter in a few important details. First, CType always attempts to convert the argument to the target type and is therefore able to convert a string into a numeric type (if the string actually contains a number, of course); DirectCast works only if the source argument can be cast to the target type and throws an InvalidCastException object otherwise. (DirectCast is unable to perform widening conversions even from Short to Integer or Single to Double.)

Second, DirectCast is slightly faster than CType, so you should use the former when you want to cast rather than convert a value. In practice, however, the speed difference between these operators is negligible. Summarizing, you can use the DirectCast keyword on three occasions:

When unboxing either a primitive value type (such as a number or a date) or a custom value type you've defined with a Structure…End Structure block

When casting a variable of a base class to a variable of a derived class—for example, a Person variable to an Employee variable or an Object variable to another reference type

When casting an object variable to an interface variable"




#3 graveyard filla   Members   -  Reputation: 583

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Posted 04 January 2007 - 07:49 AM

I see... For some reason I thought DirectCast was more limited to things with parent/child relationships, but apparently not...

Those 3 cases pretty much handle everything... When not using DirectCast, should I always use the Convert class then? E.G. the C* function have no special use case? Is that typically what you guys are doing in your production builds of your software?

Thanks again.




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