Check $strictNullComparison outside of loops

[ConnectGrid]

Might be considered a micro-optimization, but for large sheets, it could make a difference in performance. Only check the $strictNullComparison condition once, not for every single cell loop.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Instantiating Worksheets from an array are currently less than optimal due to checking a boolean condition on every single cell loop.

[MarkBaker]

I've not run any timing tests on your code yet; but when it comes to micro-optimisations, then interpolation is more efficient than the concatenation that we use here:

$this->getCell("{$currentColumn}{$startRow}")->setValue($cellValue);

Try running

$callStartTime = microtime(true);

for ($row = 1; $row <= 65535; ++$row) {
    for ($column = 'A'; $column !== 'IV'; ++$column) {
        $cellAddress = $column . $row;
    }
}

$callEndTime = microtime(true);
$concatenationCallTime = $callEndTime - $callStartTime;

echo PHP_EOL;
echo 'Call time for concatenation was ' , sprintf('%.4f', $concatenationCallTime) , ' seconds' , PHP_EOL;


$callStartTime = microtime(true);

for ($row = 1; $row <= 65535; ++$row) {
    for ($column = 'A'; $column !== 'IV'; ++$column) {
        $cellAddress = "{$column}{$row}";
    }
}

$callEndTime = microtime(true);
$interpolationCallTime = $callEndTime - $callStartTime;

echo PHP_EOL;
echo 'Call time for interpolation was ' , sprintf('%.4f', $interpolationCallTime) , ' seconds' , PHP_EOL;

to see the difference

And I'm of the growing opinion that interpolation is actually more readable