"Pavils Jurjans" <pav***@mailbox.riga.lv> wrote in message
news:uVI1vPsaGHA.3976@TK2MSFTNGP02.phx.gbl...
> Hello,
>
> I am somewhat lost in the implicit/expicit possible/impossible type
> casting in C#...
>
> I need to write a class, which among other things, must have wat to read a
> numeric value type, and internally convert it so that it could be saved in
> database as real number (float). I plan to provide property(set) interface
> for reading the value.
>
> I have counted 11 types that are "numeric" in nature. Maybe there are
> more, I don't know:
>
> SByte
> Int16
> Int32
> Int64
> Byte
> UInt16
> UInt32
> UInt64
> Decimal
> Double
> Single
>
> Obviously, it makes sense to long for a single property, that takes object
> type and then knows what to do with it. Alternative could be writing
> separate 11 properties for all the numeric types, that sounds like good
> waste of time and code.
> What I am sort of looking for, is the most correct way to do the two
> following things:
>
> 1. Validate if the input is numeric.
> my present approaches are:
> 1.1. Check if the value is a mamber of any one of the types:
> if (value is SByte || value is Int16 || value is Int32 ... ) { proceed }
> 1.2. Do it in another way:
> switch(value.GetType()+"")
>    {
>     case "System.Int16":
>     case "System.Int32":
>     case "System.Int64":
>     case "System.UInt16":
>     case "System.UInt32":
>     case "System.UInt64":
>     .....
>        proceed
>    }
>
> 2. Once we discovered that value is number, must convert the value to
> Double
> 1.1. Use implicit conversion:
> Possible only in case if I have different properties for different number
> types
> 1.2. Use explicit conversion:
> int i = 100;
> object o = i;
> double d = (double) o; // throws error "Specified cast not valid",
> although double d = (double) i;  works smoothly.
> 1.3 Use Convert.ToDouble(value)
> Seems that this works quite well. But, perhaps that is not the "fastest"
> way?
>
> Thanks for help,
>
> Pavils
>

> Let's take a step back.
>
> Where are these numbers coming from?   Does a line that reads them look
> like this:
>    int N = ReadFieldInt("Num");
> or are they all like this:
>    object obj = ReadField("Num");
>
> And if the latter, is ReadField() taking different types and forcing
> them all into an object?
>
> The reason I ask these questions is:
>  a) Doing the type identification at run-time is a slow & fragile
> process.
>  b) Doing it at compile-time is fast & safer.
>  c) It's a virtual certainty that you already know what the data type
> is.  (for example, if they are being read from a database, the database
> clearly knows what type they are.  And if you are reading a particular
> field, you know if that fields is a string or a number.)