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Introducing C# 10: File-scoped namespaces

 3 years ago
source link: https://anthonygiretti.com/2021/08/12/introducing-c-10-file-scoped-namespaces/
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Introducing C# 10: File-scoped namespaces

2021-08-12 by anthonygiretti

Introduction

C# is still evolving and C# 10 proposes a new feature : file_scoped namespaces. As its name suggests, the namespace declared in a file (without braces, but whose instruction ends with a semicolon) will apply to all elements declared in the same file. It’s practical, no more need for indentation since the opening and closing braces of the namespace disappear. There is still a limitation, only one namespace can be declared in the file, otherwise you will get a compiler error.

Example

The following code shows what is a file-scoped namespace:

namespace DemoCsharp10.Products;

public record struct Product { public string Name { get; init; } public int CategoryId { get; init; } public ProductWarranty Warranty { get; init; } }

public enum ProductWarranty { Unlimited = 0, OneYear = 1, TwoYears = 2 }

The following below is illegal:

namespace DemoCsharp10;

namespace Products //Error CS8955 Source file can not contain both file-scoped and normal namespace declarations. { public record struct Product { public string Name { get; init; } public int CategoryId { get; init; } public ProductWarranty Warranty { get; init; } }

public enum ProductWarranty { Unlimited = 0, OneYear = 1, TwoYears = 2 } }

The compiler will throw the following error:

Error CS8955 Source file can not contain both file-scoped and normal namespace declarations.

The following below is also illegal:

namespace DemoCsharp10; namespace Products; //Error CS8954 Source file can only contain one file-scoped namespace declaration.

public record struct Product { public string Name { get; init; } public int CategoryId { get; init; } public ProductWarranty Warranty { get; init; } }

public enum ProductWarranty { Unlimited = 0, OneYear = 1, TwoYears = 2 }

The compiler will throw the following error:

Error CS8954 Source file can only contain one file-scoped namespace declaration.

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