“var”对字段声明有什么区别？

Question

What's the difference between the following declarations of S and F ?

type
  TMyClass = class(TObject)
  private
    S: String;
  private var
    F: String;
  end;

The reason I'm asking is because I could use S the same way as F (without adding the var keyword).

Are they treated differently?

Answer 1

There is no difference at all. According to the documentation :

The var keyword is optional. However, if it is not used, then all field declarations must occur before any property or method declarations. After any property or method declarations, the var may be used to introduce any additional field declarations.

Answer 2

They are both Fields with the same visibility.

The var keyword is needed sometimes, when you declare fields after other declarations (like constants, inner types or even after methods and properties).

For example:

type
  TMyClass = class
  private
    FSomeField: string; //<--- this is a field, here you don't need the var clause
    const
      SOME_CONSTANT = 1;
      OTHER_CONSTANT = 2;  
    var //<---- here you need the var clause to start declaring fields
      FSomeOtherField: string; 
  end;

The var field is needed in the second case ( FSomeOtherField ) to instruct the compiler now come a series of fields declarations, but in the first case it is not needed for historical reasons, because in the first Delphi versions you can just declare Fields and there was not support for nested types or constants.