Is it generally considered bad practice for a base class constructor to return objects in its derived classes depending on input parameters? If so, what is a preferrable alternative?

Example:

Base class: Sentence
Derived classes: Sentence::Interrogative, Sentence::Declarative, Sentence::Imperative all use Sentence as a base class. 

$s = Sentence->new("This is a test.");
print ref($s); # Prints Sentence::Declarative

$s = Sentence->new("Is this a test?");
print ref($s); # Prints Sentence::Interrogative

$s = Sentence->new("Duck!");
print ref($s); # Prints Sentence::Imperative

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In reply to Base class constructor that blesses into subclass by mp

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