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World Congress 2025 • Aug 20, 2025 • Session details

C# Lowering - What is it and why should I care?

Steven Giesel

A simple C# foreach loop secretly compiles into entirely different structures depending on your data collection. Master compiler lowering to unlock a new tier of performance predictability.

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#1 about 4 min

Understanding the purpose of compiler lowering in C#

Why developers should understand compiler transformations to analyze performance and debug logic.

#2 about 4 min

Defining compiler lowering versus traditional compiling

How lowering transforms high-level language features into low-level constructs within the same language.

#3 about 1 min

Lowering the var keyword using type interference

How the compiler replaces the implicit var keyword with explicit type declarations.

#4 about 3 min

Evaluating subtle behavior changes in expression statements

How using pre-increment expression statements yields different semantics than standard property getters.

#5 about 2 min

Transforming foreach loops into while loops by the compiler

How a foreach iteration translates into a standard while loop using basic indexers.

#6 about 3 min

Analyzing foreach performance on lists versus arrays

Why iterating over lists generates state machines compared to cost-effective indexer calls for arrays.

#7 about 3 min

Diagnosing silent bugs in disposable asynchronous tasks

Why failing to await asynchronous tasks causes finally blocks to execute and incorrectly dispose resources early.

#8 about 3 min

Unpacking the yield keyword into custom state machines

How yielding elements constructs an enumerator class handling sequence position and traversal dynamically.

#9 about 6 min

Benchmarking yield iterations against prepopulated lists

Balancing memory allocation overhead in prepopulated lists against CPU cycle costs for yield iterations.

Matching moments

3:32 min

Clarifying best practice patterns during structural syntax tool discussions

Jens Claes · WWC 2023

1:55 min

Introduction to systems programming and performance in .NET

Szymon Kulec Szymon Kulec · WWC Europe 2026

4:22 min

Managing compilation performance and implementation specifics of advanced typing

Peter Kröner Peter Kröner · WWC 2022

2:50 min

Dispelling common optimization and runtime performance misconceptions

Bjarne Stroustrup · WWC 2022

2:00 min

Understanding core browser technologies and framework syntax sugar

Sasha Shynkevich · LIVE

2:07 min

Understanding JIT compilation and breakpoint de-optimization

Johannes Bechberger · LIVE

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