Pascal - Variants
Pascal supports a unique type of storage named variants. You can assign any simple type of values in a variant variable. The type of a value stored in a variant is only determined at runtime. Almost any simple type can be assigned to variants: ordinal types, string types, int64 types.
Structured types such as sets, records, arrays, files, objects and classes are not assignment-compatible with a variant. You can also assign a pointer to a variant.
Free Pascal supports variants.
Declaring a Variant
You can declare variant type like any other types using the var keyword. The syntax for declaring a variant type is −
var v: variant;
Now, this variant variable v can be assigned to almost all simple types including the enumerated types and vice versa.
type color = (red, black, white); var v : variant; i : integer; b : byte; w : word; q : int64; e : extended; d : double; en : color; as : ansistring; ws : widestring; begin v := i; v := b; v := w; v := q; v := e; v := en; v := d: v := as; v := ws; end;
The following example would illustrate the concept −
Program exVariant; uses variants; type color = (red, black, white); var v : variant; i : integer; r: real; c : color; as : ansistring; begin i := 100; v:= i; writeln('Variant as Integer: ', v); r:= 234.345; v:= r; writeln('Variant as real: ', v); c := red; v := c; writeln('Variant as Enumerated data: ', v); as:= ' I am an AnsiString'; v:= as; writeln('Variant as AnsiString: ', v); end.
When the above code is compiled and executed, it produces the following result −
Variant as Integer: 100 Variant as real: 234.345 Variant as Enumerated data: 0 Variant as AnsiString: I am an AnsiString