The string representation of the class – the asString operation is available on everything.

asString operator converts a value into a string representation. It is a type-conversion (casting) operation. It does not change the actual data type of the attribute — it only converts it in the expression result

Example:

123->asString()

It converts a value in a string form

123

Applying asString operator on Date type in a class object

Employee.allinstances->collect(x|x.DateOfBirth.asString())

Please read here onperformance when using asString.