Difference between revisions of "Nullable types"
From Free Pascal wiki
Jump to navigationJump to search (Add external link to file and adjust wording) |
|||
| Line 2: | Line 2: | ||
Nullable types are types which can have no value (can be unassigned). | Nullable types are types which can have no value (can be unassigned). | ||
| − | One such type in Pascal is [[Pointer]] type which can have [[Nil|<syntaxhighlight lang="pascal" | + | One such type in Pascal is [[Pointer]] type which can have [[Nil|<syntaxhighlight lang="pascal" inline>nil</syntaxhighlight>]] value which means that it isn't assigned to any specific address. |
Same behavior can be implemented using [[Generics|generic types]] and advanced records with [[Operator overloading|operator overloading]]. | Same behavior can be implemented using [[Generics|generic types]] and advanced records with [[Operator overloading|operator overloading]]. | ||
Latest revision as of 17:19, 6 August 2022
│
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 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
The standard nullable type in Object Pascal is Variant.
