Performance implications of default struct equality in C#

If you’re familiar with C#, then you most likely heard that you should always override Equals and GetHashCode for custom structs for performance reasons. To better understand the importance and the rationale behind this advice we’re going to look at the default behavior to see why and where the performance hit comes from. Then we’ll…

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Dissecting new generic constraints in C# 7.3

During the last Build conference, Microsoft has announced the next version of Visual Studio with C# 7.3 support. This is yet another minor language update with some quite interesting features. The main change was related to generics, starting from C# 7.3 there 3 more constraints: unmanaged, System.Enum and System.Delegate. The unmanaged constraint The unmanaged constraint…

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Performance traps of ref locals and ref returns in C#

The C# language from the very first version supported passing arguments by value or by reference. But before C# 7 the C# compiler supported only one way of returning a value from a method (or a property) – returning by value. This has been changed in C# 7 with two new features: ref returns and…

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Nullable types arithmetic and null-coalescing operator precedence

Here is a simple question for you: which version of a GetHashCode() is correct and what performance impact does the incorrect version have? public struct Struct1{    public int N { get; }    public string S { get; }    public Struct1(int n, string s = null) { N = n; S = s; }     public override int GetHashCode() =>         N ^         S?.GetHashCode()…

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The ‘in’-modifier and the readonly structs in C#

C# 7.2 got two very important features for high-performance scenarios — the readonly structs and the in parameters. But to understand why this additions are so important and how they’re related to each other we should look back in history. As you probably know, the .NET ecosystem has two family of types — the value…

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Dissecting the async methods in C#

The async series Dissecting the async methods in C#. Extending the async methods in C#. The performance characteristics of the async methods in C#. One user scenario to rule them all. The C# language is great for developer’s productivity and I’m glad for the recent push towards making it more suitable for high-performance applications. Here…

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Dissecting the tuples in C# 7

System.Tuple types were introduced in .NET 4.0 with two significant drawbacks: (1) tuple types are classes and (2) there was no language support for constructing/deconstructing them. To solve these issues, C# 7 introduces new language feature as well as a new family of types (*). Today, if you need to glue together two values to…

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Dissecting the pattern matching in C# 7

C# 7 finally introduced a long-awaited feature called “pattern matching”. If you’re familiar with functional languages like F# you may be slightly disappointed with this feature in its current state, but even today it can simplify your code in a variety of different scenarios. Every new feature is fraught with danger for a developer working…

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Dissecting the local functions in C# 7

The Local functions is a new feature in C# 7 that allows defining a function inside another function. When to use a local function? The main idea of local functions is very similar to anonymous methods: in some cases creating a named function is too expensive in terms of cognitive load on a reader. Sometimes…

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A common execution path optimization

Today I want to talk about one interesting optimization pattern that you may face in framework code or in high-performance libraries. The idea is simple: suppose you have a commonly used method that has two execution paths – one is very common and simple, and the second one takes longer to execute, has more steps…

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