The .NET Standard library exists to address the fragmentation and compatibility issues that arose from having multiple .NET implementations, such as .NET Framework, .NET Core, and Xamarin. Here are the key reasons for its existence:
1. Unified API Specification
.NET Standard is a formal specification of APIs that all .NET implementations must support. This ensures that a library targeting .NET Standard can be used across different .NET platforms without modification. It defines a consistent set of APIs that are available on all .NET implementations, thereby unifying the Base Class Libraries (BCL) across these platforms[1][2][3][4][5].
2. Code Sharing
By targeting .NET Standard, developers can create libraries that are reusable across different .NET environments. This eliminates the need to write and maintain separate versions of a library for each .NET implementation. For example, a library built for .NET Standard can be used in applications running on .NET Framework, .NET Core, and Xamarin, facilitating code sharing and reducing duplication[1][2][3][4][5].
3. Portability
.NET Standard enhances the portability of code by providing a common set of APIs that work across various platforms. This is particularly useful for developers who need to support multiple platforms, such as Windows, Linux, macOS, iOS, and Android. It simplifies the development process by allowing a single codebase to run on different operating systems[1][2][3][4][5].
4. Backward Compatibility
Each version of .NET Standard includes all APIs from previous versions, along with new APIs. This ensures backward compatibility, allowing libraries targeting an older version of .NET Standard to work with newer .NET implementations. This versioning strategy helps maintain compatibility and eases the transition to newer versions of .NET[1][2][3][4][5].
5. Replacement for Portable Class Libraries (PCL)
.NET Standard replaces the older Portable Class Libraries (PCL) approach, which had limitations in terms of API availability and platform support. PCLs required developers to select specific platforms during library creation, which often resulted in a limited set of common APIs. .NET Standard overcomes these limitations by providing a more comprehensive and unified API set[3][4][7].
