Default keyword for generic types in C Sharp (C#) - Cheat Sheet & Quick Revision

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beginner

What does the default keyword do for generic types in C#?

The default keyword returns the default value for a generic type parameter. For reference types, it returns null. For value types, it returns zero or equivalent (like 0 for numbers, false for bool).

beginner

How do you use default to initialize a generic variable T?

You write T variable = default; or T variable = default(T);. Both assign the default value for type T.

intermediate

What is the default value of a generic type parameter T if T is a struct?

If T is a struct (a value type), default(T) returns a struct with all fields set to their default values (like zero for numbers, false for bool).

intermediate

Can default be used with nullable types in generics?

Yes. For nullable types like int?, default returns null, which is the default for nullable types.

beginner

Why is default useful in generic methods or classes?

Because generic types can be any type, default lets you safely get a default value without knowing the exact type. This avoids errors and makes code flexible.

What does default(T) return if T is a reference type?

A 0

B null

C false

D An empty object

For reference types, default(T) returns null.

How can you write the default value for a generic type T in C# 7.1 or later?

A <code>default</code>

B <code>null</code>

C <code>new T()</code>

D <code>default(T)</code>

Since C# 7.1, you can use the simplified default literal without specifying the type.

What is the default value of bool when used as a generic type parameter?

A null

B true

C false

D 1

The default value for bool is false.

If T is int? (nullable int), what does default(T) return?

A 0

B false

C An exception

D null

Nullable types default to null.

Why might you prefer default over new T() in generic code?

A <code>default</code> works even if <code>T</code> has no parameterless constructor

B <code>new T()</code> always works

C <code>default</code> creates a new object

D <code>new T()</code> returns null

new T() requires T to have a parameterless constructor, but default does not.

Explain how the default keyword works with generic types in C#.

Think about what happens when you don't know the exact type.

Describe a situation where using default is better than new T() in generic programming.

Consider constructor requirements.