Add formula in v3.3.0

src/Spout/Common/Entity/Cell.php

@@ -139,6 +139,9 @@ class Cell
      */
     protected function detectType($value)
     {
+        if (CellTypeHelper::isFormula($value)) {
+            return self::TYPE_FORMULA;
+        }
         if (CellTypeHelper::isBoolean($value)) {
             return self::TYPE_BOOLEAN;
         }
@@ -198,6 +201,14 @@ class Cell
         return $this->type === self::TYPE_DATE;
     }
 
+    /**
+     * @return bool
+     */
+    public function isFormula()
+    {
+        return $this->type === self::TYPE_FORMULA;
+    }
+
     /**
      * @return bool
      */

src/Spout/Common/Helper/CellTypeHelper.php

@@ -60,9 +60,19 @@ class CellTypeHelper
      */
     public static function isDateTimeOrDateInterval($value)
     {
-        return (
+        return ($value instanceof \DateTimeInterface ||
-            $value instanceof \DateTimeInterface ||
             $value instanceof \DateInterval
         );
     }
+
+    /**
+     * Returns whether the given value looks like a formula
+     *
+     * @param $value
+     * @return bool whether the given value looks like a formula
+     */
+    public static function isFormula($value)
+    {
+        return (strpos($value, '=') === 0);
+    }
 }

src/Spout/Writer/XLSX/Manager/WorksheetManager.php

@@ -179,7 +179,7 @@ EOD;
      * @throws InvalidArgumentException If the given value cannot be processed
      * @return RegisteredStyle
      */
-    private function applyStyleAndRegister(Cell $cell, Style $rowStyle) : RegisteredStyle
+    private function applyStyleAndRegister(Cell $cell, Style $rowStyle): RegisteredStyle
     {
         $isMatchingRowStyle = false;
         if ($cell->getStyle()->isEmpty()) {
@@ -228,7 +228,9 @@ EOD;
         $cellXML = '<c r="' . $columnLetters . $rowIndexOneBased . '"';
         $cellXML .= ' s="' . $styleId . '"';
 
-        if ($cell->isString()) {
+        if ($cell->isFormula()) {
+            $cellXML .= ' ><f>' . substr($cell->getValue(), 1) . '</f></c>';
+        } elseif ($cell->isString()) {
             $cellXML .= $this->getCellXMLFragmentForNonEmptyString($cell->getValue());
         } elseif ($cell->isBoolean()) {
             $cellXML .= ' t="b"><v>' . (int) ($cell->getValue()) . '</v></c>';