What is CLS (Common Language Specification) in .NET?
💡 Concept Name
CLS (Common Language Specification)
📘 Quick Intro
CLS defines a set of rules and guidelines that .NET languages must follow to ensure interoperability. Code that follows CLS can be used across all .NET languages like C#, F#, and VB.NET.
🧠 Analogy / Short Story
Think of CLS as a "universal handshake" between .NET languages. If everyone follows the same handshake rules, they can all understand and work with each other—regardless of their native language (C#, F#, etc.).
🔧 Technical Explanation
- 📜 CLS is a subset of the Common Type System (CTS).
- 🔁 It defines the minimal features needed for cross-language compatibility.
- 🚫 Certain C# features like unsigned types (`uint`, `ulong`) are not CLS-compliant.
- ✔ CLS-compliant code is more reusable and accessible from other .NET languages.
- 🧪 Use `[CLSCompliant(true)]` attribute to enforce compliance during compilation.
🎯 Purpose & Use Case
- ✅ Enable code sharing across different .NET languages.
- ✅ Ensure public APIs can be consumed universally.
- ✅ Promote standardization and interoperability within large teams/projects.
💻 Real Code Example
Enforce CLS compliance and avoid non-compliant types like `uint`:
[assembly: CLSCompliant(true)]
public class MathLib
{
// ❌ Not CLS-compliant (uint)
// public uint Add(uint a, uint b) => a + b;
// ✅ CLS-compliant
public int Add(int a, int b) => a + b;
}
❓ Interview Q&A
Q1: What is CLS in .NET?
A: A specification that defines rules for language interoperability.
Q2: Why is CLS needed?
A: To ensure code written in one .NET language can be used in another.
Q3: Is `uint` CLS-compliant?
A: No.
Q4: How do you enable CLS checks in code?
A: Use `[assembly: CLSCompliant(true)]` attribute.
Q5: Is CLS a runtime or compile-time feature?
A: Compile-time.
📝 MCQs
Q1. What does CLS stand for in .NET?
- Common Library System
- Code Linking Structure
- Common Language Specification
- Core Language Service
Q2. What is the goal of CLS?
- Code optimization
- Low memory usage
- Language interoperability
- Runtime validation
Q3. Which type is NOT CLS-compliant?
- int
- string
- uint
- bool
Q4. What attribute enables CLS compliance checking?
- [CLSCheck]
- [assembly: CLSCompliant(true)]
- [VerifyCLS]
- [Compliant]
Q5. CLS is a subset of?
- JIT Compiler
- Common Language Runtime
- Common Type System
- Intermediate Language
💡 Bonus Insight
When building public libraries or SDKs meant for wide reuse, making your code CLS-compliant ensures that all .NET languages can consume it. It's a best practice even if you're only writing in one language initially.
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