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ReverseString

Function ReverseString( const AText : string) : string

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := ReverseString('ABC-123'); // 321-CBA
end;

Usage​

Use ReverseString to reverse the UTF-16 code units in a string. It is suitable for code-unit-oriented text, but it can split surrogate pairs and combining-character sequences, so do not use it when user-perceived Unicode characters must remain intact.

Parameters and return value

AText is not modified.

Additional Technical Info​

ReverseString allocates a result with the same Delphi Length as AText, then copies source positions from High(AText) down to Low(AText). It reverses UTF-16 Char code units, not user-perceived Unicode characters.

The example is fictional and source-reviewed only.

Important Unicode behavior

  • A supplementary Unicode character is represented by a UTF-16 surrogate pair. Reversing its two code units produces an invalid pair.
  • A base character followed by combining marks has its code units reversed, so the visual grapheme is not preserved.
  • Emoji sequences joined by variation selectors or zero-width joiners are not treated atomically.
  • Applying ReverseString twice restores the original code-unit sequence, even when the once-reversed intermediate text is not valid/meaningful Unicode.

Use this function for code-unit-oriented ASCII or controlled BMP text. It is not a locale-aware reversal, word reversal or grapheme-cluster reversal.

Performance and concurrency

Runtime is linear in UTF-16 length with one result allocation. No shared state is read.

External references

Created 2026-07-15