Runtime cost of dynamic type resolution in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is dynamic type resolution in C#?

Dynamic type resolution is when the program determines the type of an object at runtime instead of compile time, allowing more flexible code but with some performance cost.

beginner

Why does dynamic type resolution have a runtime cost?

Because the program must look up the actual type and method to call during execution, which takes extra time compared to compile-time type checking.

intermediate

How does C# implement dynamic type resolution internally?

C# uses the Dynamic Language Runtime (DLR) which performs method binding and type checks at runtime using reflection and caching to improve performance.

intermediate

What is a common performance impact of using 'dynamic' in C#?

Using 'dynamic' can slow down method calls because the runtime must resolve the method to invoke each time, unlike static calls which are direct.

advanced

How can you reduce the runtime cost of dynamic type resolution?

You can cache dynamic call sites or avoid excessive use of 'dynamic' in performance-critical code to reduce overhead.

What does dynamic type resolution mean in C#?

A Using only static types

B Determining object type at compile time

C Ignoring object types

D Determining object type at runtime

Dynamic type resolution means the program figures out the object's type while running, not before.

Which C# feature enables dynamic type resolution?

A const keyword

B dynamic keyword

C var keyword

D readonly keyword

The 'dynamic' keyword tells C# to resolve types at runtime.

What is a main cause of runtime cost when using dynamic types?

A Compile-time optimization

B Static type checking

C Runtime method lookup

D Memory allocation only

The runtime must find the correct method to call, which takes extra time.

Which runtime component helps with dynamic type resolution in C#?

A Dynamic Language Runtime (DLR)

B Common Language Runtime (CLR)

C Just-In-Time compiler (JIT)

D Garbage Collector (GC)

The DLR manages dynamic operations and type resolution.

How can you improve performance when using dynamic types?

A Cache dynamic call sites

B Use more dynamic variables

C Avoid static typing

D Disable runtime checks

Caching reduces repeated runtime lookups, improving speed.

Explain what runtime cost means in the context of dynamic type resolution in C#.

Think about what happens when the program decides types while running.

Describe ways to reduce the performance cost when using dynamic types in C#.

Consider how to avoid repeated work at runtime.

Practice

1. What does dynamic keyword in C# do at runtime?

easy

A. It performs type checking at compile time

B. It prevents any type errors completely

C. It delays type checking until the program runs

D. It converts all types to strings automatically

Solution

1. Step 1: Understand the role of dynamic

   The dynamic keyword tells C# to skip compile-time type checking for that variable.

2. Step 2: Identify when type checking happens

   Type checking for dynamic variables happens only when the program runs, not before.

3. Final Answer:

   It delays type checking until the program runs -> Option C

4. Quick Check:

   Dynamic = runtime type check [OK]

Hint: Dynamic means check types only when running [OK]

Common Mistakes:

• Thinking dynamic checks types at compile time
• Believing dynamic prevents all errors
• Assuming dynamic converts types automatically

2. Which of the following is the correct syntax to declare a dynamic variable in C#?

easy

A. dynamic = 5 x;

B. var x = dynamic 5;

C. int dynamic x = 5;

D. dynamic x = 5;

Solution

1. Step 1: Recall dynamic variable declaration syntax

   In C#, you declare a dynamic variable by writing dynamic followed by the variable name and value.

2. Step 2: Check each option's syntax

   dynamic x = 5; matches the correct syntax: dynamic x = 5;. Others have incorrect order or keywords.

3. Final Answer:

   dynamic x = 5; -> Option D

4. Quick Check:

   Correct syntax = dynamic x = value [OK]

Hint: Use 'dynamic' before variable name [OK]

Common Mistakes:

• Putting 'dynamic' after 'var'
• Mixing 'int' and 'dynamic' keywords
• Incorrect order of assignment

3. What will be the output of this C# code?

dynamic x = 10;
dynamic y = "20";
Console.WriteLine(x + y);

medium

A. 1020

B. Runtime exception

C. 30

D. Compile-time error

Solution

1. Step 1: Analyze the types of variables

   Variable x is an integer 10, and y is a string "20".

2. Step 2: Understand dynamic addition behavior

   With dynamic types, the + operator at runtime performs string concatenation when one operand is a string, resulting in "1020".

3. Final Answer:

   1020 -> Option A

4. Quick Check:

   dynamic int + string = concatenation "1020" [OK]

Hint: Dynamic number + string = string concatenation [OK]

Common Mistakes:

• Expecting a runtime exception
• Thinking it adds numerically to 30
• Assuming compile-time error

4. Identify the error in this code snippet using dynamic types:

dynamic a = 5;
dynamic b = "hello";
var result = a - b;
Console.WriteLine(result);

medium

A. Runtime exception due to invalid operation

B. No error, outputs 0

C. Compile-time type mismatch error

D. Syntax error in variable declaration

Solution

1. Step 1: Check operation between dynamic variables

   Subtracting an integer and a string is invalid at runtime.

2. Step 2: Determine error type

   Since types are dynamic, error appears only when running, causing a runtime exception.

3. Final Answer:

   Runtime exception due to invalid operation -> Option A

4. Quick Check:

   Invalid dynamic operation = runtime exception [OK]

Hint: Invalid dynamic operations fail at runtime, not compile time [OK]

Common Mistakes:

• Expecting compile-time error
• Assuming subtraction works with string
• Ignoring runtime exceptions

5. You want to improve performance in a C# program that uses many dynamic variables. Which approach reduces runtime cost of dynamic type resolution?

hard

A. Avoid testing dynamic code to save time

B. Replace dynamic variables with explicit static types where possible

C. Add more dynamic variables to delay errors

D. Use dynamic variables everywhere for flexibility

Solution

1. Step 1: Understand runtime cost of dynamic

   Dynamic variables cause extra work at runtime to check types, slowing performance.

2. Step 2: Choose optimization strategy

   Replacing dynamic with static types lets compiler check types early, improving speed.

3. Final Answer:

   Replace dynamic variables with explicit static types where possible -> Option B

4. Quick Check:

   Static types reduce dynamic runtime cost [OK]

Hint: Use static types to speed up dynamic-heavy code [OK]

Common Mistakes:

• Thinking more dynamic variables improve speed
• Ignoring testing importance
• Believing dynamic has no runtime cost