refactoring

[githubjeka]

For yiisoft#8505

[lennartvdd]

I like the cleanliness of your method, but I would definately keep naming the last param $defaultOperator instead of just $operator since it's more descriptive and less likely to cause confusion about the intended purpose.

The regex in the original method is more efficient since it only has to ever scan the first 2 chars at most. Even though it's a micro optimisation, the original method is about 40% faster than your version, so I think we should leave it as is.