What are nullable reference types in C#?
💡 Concept: Nullable Reference Types in C#
Nullable reference types help developers express whether a reference variable can be null or not, reducing null reference exceptions.
📘 Quick Intro
Introduced in C# 8, nullable reference types add syntax and compiler checks for safer code.
🧠 Analogy
Think of nullable reference types as warning signs telling you which variables might be empty, helping avoid crashes.
🔧 Technical Explanation
- Non-nullable references must always point to an object.
- Nullable references are declared with a question mark (e.g., string?).
- The compiler warns about possible null assignments and dereferences.
- Helps catch null-related bugs at compile time.
- Can be enabled or disabled via project settings.
🎯 Use Cases
- ✅ Improving code safety in large projects.
- ✅ Avoiding runtime null reference exceptions.
- ✅ Enabling better static analysis and tooling.
- ✅ Clarifying intent of nullability in APIs.
💻 Code Example
#nullable enable
string? nullableString = null; // Allowed
string nonNullableString = "Hello";
// Compiler warning if assigning null to nonNullableString
if (nullableString != null) {
Console.WriteLine(nullableString.Length);
}
❓ Interview Q&A
Q1: What are nullable reference types?
A: Reference types that can explicitly be null or non-null.
Q2: When were they introduced?
A: C# 8.0.
Q3: How do you declare a nullable reference?
A: By appending '?' to type.
Q4: What benefit do they provide?
A: Helps catch null-related errors at compile time.
Q5: Can they be disabled?
A: Yes, via project settings.
Q6: Are value types nullable?
A: Nullable value types are separate concept.
Q7: Does this eliminate all null exceptions?
A: Helps reduce but not eliminate.
Q8: How does compiler warn about null?
A: With warnings during compilation.
Q9: Can APIs indicate nullability?
A: Yes, improving contract clarity.
Q10: Are nullable reference types backward compatible?
A: Yes.
📝 MCQs
Q1. What are nullable reference types?
- Value types
- Reference types that can be null or not
- Static types
- Const types
Q2. When were nullable reference types introduced?
- C# 6.0
- C# 7.0
- C# 8.0
- C# 9.0
Q3. How to declare a nullable reference?
- Use ref
- Use out
- Append ?
- Use const
Q4. What benefit do nullable reference types provide?
- Runtime check
- Catch null errors at compile time
- Ignore null
- Force null
Q5. Can nullable reference types be disabled?
- No
- Yes
- Sometimes
- Always
Q6. Are value types nullable?
- Yes
- No
- Nullable value types are separate
- Unknown
Q7. Does nullable reference types eliminate all null exceptions?
- Yes
- No
- Maybe
- Sometimes
Q8. How does compiler warn about null?
- With errors
- With warnings
- No warning
- With exceptions
Q9. Can APIs indicate nullability?
- No
- Yes
- Maybe
- Rarely
Q10. Are nullable reference types backward compatible?
- No
- Yes
- Sometimes
- Never
💡 Bonus Insight
Nullable reference types are a powerful feature that improves code safety and clarity in C#.
📄 PDF Download
Need a handy summary for your notes? Download this topic as a PDF!