Using properties in switch statement cases?

Question

I have a switch statement in one class that generates Command objects, based on if a certain line in a code file matches the particular code for that Command object.

like this:

switch (line):
{
   case "#CODE1":
      return new Command1();
   case "#CODE2":
      return new Command2();
}

I want to turn it into something like this:

switch (line):
{
   case Command1.Code:
      return new Command1();
   case Command2.Code:
      return new Command2();
}

I tried it by creating a public static property of Command1, but the compiler complains...

Is there a way to do something along this intent, that the compiler won't complain about?

Answer 1

I think you can do this only with constants... so if it's possible for you, use constant fields instead of public static properties. The difference is that it's treated like a literal at compile time, so if the value changes, you would need to recompile all assemblies that reference the constant.

Answer 2

Switch only works on numeric types and string types, not properties. You can try defining a public string constant on your Command1 and Command2 class, which you should be able to switch on instead.

public class Command1 
{
   public string const Code = "#CODE1";
}

Answer 3

since you are working with strings I'm not sure if it's the best approach, but using enums works for me

enum CommandEnum { CommandOne, ComandTwo, CommandN }
//...

CommandEnum myCommand;
//...
switch (myCommand)
{
  case myCommand.CommandOne:
       return new Command1();
  case myCommand.CommandTwo:
       return new Command2();
  //...
}

Answer 4

I think your problem is you need to instantiate your objects before you can determine their property values.

I'm assuming you have a code file with tokenized instructions, like:

#CODE1
#CODE2

and you want a class to read each line of your file and then perform whichever instructions the tokens define.

You got it to work, but instead of doing a direct string comparison to the token in the file, you want the value of the token stored in a property of your objects? The problem with that approach is you have to create a new instance of your object (commands 1 and 2) before you can refer to their property values.

If I understand what you've done and what you want to do, I think your solution was fine the way it was. I'm not 100% sure I really understand what you want to do, though, or why.

HTH

Answer 5

If you want to check against properties on a class. I'm assuming that you probably want to be able to change those properties and check accordingly. You'll have to use an if, else if, else if type statement.

If you've got a jones to use a switch statement, you're SOL unless you're checking an integral type against constant values. if, else if, else if blocks are ugly, but it'll do what you're looking for.

Answer 6

You could always fall back on the tried and true if / else block

 if (line == Command1.Code)
  return new Command1();
 else if (line == Command2.Code)
  return new Command2();

That's not so evil, is it?