Nullable types

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 and its code can be seen in the GitLab repository: 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

• FPC GitLab Repository nullable.pp
• Nullables in Free Pascal and Delphi

From the Free Pascal wiki, page "Nullable types", as it stood on 2022-08-06 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.