Clear
procedure Clear;
Example
procedure ScriptEvent(var Value: variant);
var
Text: TJSONString;
begin
Text := TJSONString.Create;
try
Text.Value := 'retained';
Text.Clear;
Value := Text.IsNull; // True; Text.Value still contains retained.
finally
Text.Free;
end;
end;
Usage
Clears a JSON value using its runtime class's null-marking or owned-child erasure behaviour.
Additional Technical Info
Clear is virtual. On an ordinary scalar descendant, the base implementation sets the stored null flag to True; it does not erase Name or the class-specific payload. TJSONString.Value, TJSONBoolean.Value and the native numeric fields therefore retain their previous data even though null-aware AsString becomes blank. Assigning a valid payload later normally clears null state and reveals/replaces the stored value.
Runtime dispatch materially changes the operation for containers. TJSONArray.Clear and TJSONObject.Clear call their Erase implementation, freeing every owned child and invalidating all borrowed child references. They do not invoke the base null marker or change Name; their null reader always returns False. TJSONNull has no payload and always reports null, so clearing it is semantically idempotent.
The receiver remains allocated. A directly created receiver remains script-owned; clearing a parent-owned child never transfers ownership. The operation is synchronous and has no locking. Container clearing is linear in child count and recursively releases descendant trees; scalar clearing is constant-time.
No exception is expected for a live scalar. Container destruction/finalization failures are not suppressed. A nil or already freed script object cannot be used. Because the script NotNull property is misregistered, verify the result with IsNull, not NotNull.
Related entries
Created 2026-07-15