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
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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;
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The following statements are completely equivalent:
TheCustomer.Name := 'Michael';
TheCustomer.Flight := 'PS901';
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and
With TheCustomer do
begin
Name := 'Michael';
Flight := 'PS901';
end;
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The statement
With A,B,C,D do Statement;
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is equivalent to
With A do
With B do
With C do
With D do Statement;
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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 = 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.
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The output of this program is
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;
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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.