The With statement

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#### 13.2.8 The With statement

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

_________________________________________________________________________________________________________
With statement
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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 field or method of the record or object or class. If so, then that field 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 first, i. e., when the compiler encounters a variable reference, it will first check if it is a field 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 = ^Ar;
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 definitions 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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