Quick start manual

5-26 Delphi Language Guide
Structured types
type
TShapeList = (Rectangle, Triangle, Circle, Ellipse, Other);
TFigure = record
case TShapeList of
Rectangle: (Height, Width: Real);
Triangle: (Side1, Side2, Angle: Real);
Circle: (Radius: Real);
Ellipse, Other: ();
end;
For each record instance, the compiler allocates enough memory to hold all the fields
in the largest variant. The optional tag and the constantLists (like Rectangle, Triangle,
and so forth in the last example) play no role in the way the compiler manages the
fields; they are there only for the convenience of the programmer.
The second reason for variant parts is that they let you treat the same data as
belonging to different types, even in cases where the compiler would not allow a
typecast. For example, if you have a 64-bit Real as the first field in one variant and a
32-bit Integer as the first field in another, you can assign a value to the Real field and
then read back the first 32 bits of it as the value of the Integer field (passing it, say, to a
function that requires integer parameters).
File types
A file a sequence of elements of the same type. Standard I/O routines use the
predefined TextFile or Text type, which represents a file containing characters
organized into lines. For more information about file input and output, see
Chapter 8, “Standard routines and I/O”.
To declare a file type, use the syntax
type fileTypeName = file of type
where fileTypeName is any valid identifier and type is a fixed-size type. Pointer
types—whether implicit or explicit—are not allowed, so a file cannot contain
dynamic arrays, long strings, classes, objects, pointers, variants, other files, or
structured types that contain any of these.
For example,
type
PhoneEntry = record
FirstName, LastName: string[20];
PhoneNumber: string[15];
Listed: Boolean;
end;
PhoneList = file of PhoneEntry;
declares a file type for recording names and telephone numbers.