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Bits

property Bits[Index: Integer]: Boolean read write;

Example​

procedure ScriptEvent(var Value: variant);
var
  Flags: TBits;
begin
  Flags := TBits.Create;
  try
    Flags.Bits[7] := True;  // grows Size from 0 to 8
    Flags.Bits[3] := False;
    Value := Flags.Bits[7];
  finally
    Flags.Free;
  end;
end;

Usage​

Bits reads or writes one Boolean flag, with strict read bounds and automatic logical growth on non-negative writes.

Additional Technical Info​

Bits provides zero-based indexed access to the packed flags. Delphi declares it as the default property, but using the explicit Bits[Index] form makes the operation and its growth behavior clearer in Velox scripts.

A read succeeds only when Index is between zero and Size minus one. A negative index, an index equal to Size, or any larger index raises EBitsError; reading never grows the set and an empty set has no readable index.

A write also rejects a negative index. A non-negative index at or beyond the current end first sets Size := Index + 1, then writes the requested Boolean. This happens for both True and False, so Flags.Bits[1000000] := False still creates a million-and-one-bit logical set and can allocate substantial memory. Intermediate newly allocated words are initialized false.

The bit is selected by an Integer-word mask. Reads and writes are constant-time after any required growth. Growth can allocate and copy storage and can therefore raise an allocation exception in addition to EBitsError for invalid indices.

Shrinking Size does not necessarily clear bits outside the new logical range. When the shrink stays within retained word storage, expanding again can reveal the previous values. If a stable reset is required, assign the relevant positions false before shrinking, set Size := 0 to free all storage, or explicitly initialize the expanded range.

The property is mutable and unsynchronised. A simultaneous resize and access is unsafe. Do not retain or share the object across concurrent Velox executions.

The source-reviewed example demonstrates write-driven growth and caller-owned lifetime. It was not executed by the documentation workflow.

External references

Created 2026-07-15