9.2.7 The With statement

The with statement serves to access the elements of a record or object or class, without having to specify the name of the each time. The syntax for a with statement is

_________________________________________________________________________________________________________ With statement
-- --with statement -|-variable reference---do- statement -------------------
6------,--------
___________________________________________________________________

The variable reference must be a variable of a record, object or class type. In the with statement, any variable reference, or method reference is checked to see if it is a eld or method of the record or object or class. If so, then that eld is accessed, or that method is called. Given the declaration:

Type Passenger = Record
       Name : String[30];
       Flight : String[10];
       end;
Var TheCustomer : Passenger;

The following statements are completely equivalent:

TheCustomer.Name := 'Michael';
TheCustomer.Flight := 'PS901';

and

With TheCustomer do
  begin
  Name := 'Michael';
  Flight := 'PS901';
  end;

The statement

With A,B,C,D do Statement;

is equivalent to

With A do
With B do
With C do
With D do Statement;

This also is a clear example of the fact that the variables are tried last to rst, i.e., when the compiler encounters a variable reference, it will rst check if it is a eld or method of the last variable. If not, then it will check the last-but-one, and so on. The following example shows this;

Program testw;
Type AR = record
      X,Y : Longint;
     end;
     PAR = Record;

Var S,T : Ar;
begin
  S.X := 1;S.Y := 1;
  T.X := 2;T.Y := 2;
  With S,T do
    WriteLn (X,' ',Y);
end.

The output of this program is

2 2

Showing thus that the X,Y in the WriteLn statement match the T record variable.

Remark: When using a With statement with a pointer, or a class, it is not permitted to change the pointer or the class in the With block. With the denitions of the previous example, the following illustrates what it is about:

Var p : PAR;

begin
  With P^ do
   begin
   // Do some operations
   P:=OtherP;
   X:=0.0;  // Wrong X will be used !!
   end;

The reason the pointer cannot be changed is that the address is stored by the compiler in a temporary register. Changing the pointer won't change the temporary address. The same is true for classes.

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