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RegExReplace

Function RegExReplace( const ARegExpr, AInputStr, AReplaceStr : string) : boolean

Example​

procedure ScriptEvent(var Value: variant);
var
  Input: String;
begin
  Input := 'Order 1007';
  if RegExReplace('[0-9]+', Input, '####') then
    Value := Input; // still 'Order 1007'
end;

Usage​

RegExReplace reports whether a regex matches, but currently discards the computed replacement and leaves the input unchanged.

Parameters

ParameterMeaning
ARegExprVelox/PCRE pattern.
AInputStrRead-only input text. It is never changed.
AReplaceStrReplacement expression passed to Velox only when a match is first found. Any resulting text is discarded.

Return value

The Boolean result of TRegEx.IsMatch(AInputStr, ARegExpr): True for a non-empty match and False otherwise. It does not indicate that observable replacement occurred.

Important behavior and quirks

  • No successful call changes AInputStr or returns replaced text.
  • A matched input is scanned twice: once by IsMatch and again by Replace.
  • An unmatched input does not evaluate replacement processing beyond the first match test.
  • The default regex options include roNotEmpty; empty matches alone are excluded.
  • Replacement syntax, including group substitutions, is still evaluated when a match is found. A malformed or unsupported replacement can therefore raise an error even though replacement text is never returned.

Additional Technical Info​

RegExReplace currently acts as an expensive Boolean match test. When a match exists it computes a replaced string internally, but discards that string. AInputStr is declared const, so neither the caller's value nor any return string can receive the replacement.

The example is fictional and source-reviewed only. It demonstrates the current defect; do not use this function when transformed text is required.

Exact implementation

Result := TRegEx.IsMatch(AInputStr, ARegExpr);
if Result then
  TRegEx.Replace(AInputStr, ARegExpr, AReplaceStr);

Delphi TRegEx.Replace is a function returning a new string. The Velox wrapper ignores that return value.

Recommended selection

Use RegExMatch when only a Boolean test is required. There is currently no working public regex replacement function in this entry. For exact literal replacement, use StringReplaceAll or StringReplaceFirst as appropriate.

Errors, performance and concurrency

Pattern and replacement exceptions propagate. Matched inputs allocate a replacement result that is immediately released, so the function can consume time and memory without producing transformed output. Regex backtracking risks still apply. Per-call regex objects are local.

External references

Created 2026-07-15