What is the purpose of new() while declaration of a generic class?

Question

What is the purpose of new() while declaration of BaseEntityCollection class?
If I'm going to remove it, I got an error with the following message "T must be a non-abstract type with a public parameterless constructor in order to use it as parameter ..."

public abstract partial class BaseEntityCollection<T> : 
       List<T> where T : BaseEntity, new()

Answer 1

Writing new() forces the parameter to have a default constructor.

Without it, you can't write new T().
Your error happens when you try to pass a non-new() type as a new()'d parameter.

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Also, do not inherit List<T>.
Instead, you should inherit Collection<T>, which is designed for inheritance.