Nullable types

│ English (en) │ suomi (fi) │

Nullable types are types which can have no value (can be unassigned). One such type in Pascal is Pointer type which can have nil value which means that it isn't assigned to any specific address. Same behavior can be implemented using generic types and advanced records with operator overloading.

The Nullable unit is part of FPC since 3.2.2. Its code in the GitLab: nullable.pp.

Then you can define nullable types like:

NullableChar = TNullable<Char>;
NullableInteger = TNullable<Integer>;
NullableString = TNullable<string>;

See also

• How to use nullable types

The standard nullable type in Object Pascal is Variant.

• Variant

External links

• Nullables in Free Pascal and Delphi