how does C# know what Path class is without giving me have a line 'using System.IO'?

Question

I have this snippet of code. Why does C# know what Path class is without giving me an error given that Path is in the System.IO, logically, I should include it. However, Visual Studio 2022 did not yell at that. And another question is does using Some.Namespace automatically import other files in the file structure in C#? Like in PHP, when we want to use some classes from another file, we have to import that file use require_once or in Python, we use the import statement.

using System.Text.Json;

namespace ContosoCrafts.Website.Services
{
    public class JsonFileProductService
    {

        public JsonFileProductService(IWebHostEnvironment webHostEnvironment)
        {
            WebHostEnvironment = webHostEnvironment;
        }

        public IWebHostEnvironment WebHostEnvironment { get; }

        private string JsonFileName
        {
            get { return Path.Combine(WebHostEnvironment.WebRootPath, "data", "products.json"); }
        }
    }

}

This can only be explained with the "implicit usings" feature of .Net 6. — freakish, Sep 06 '22 at 13:27
.net 6 has _implicit usings_. see https://dotnetcoretutorials.com/2021/08/31/implicit-using-statements-in-net-6/ — Nsevens, Sep 06 '22 at 13:27
Looks like you're experiencing the magic of [implicit using directives](https://learn.microsoft.com/en-us/dotnet/core/tutorials/top-level-templates#implicit-using-directives) — Mathias R. Jessen, Sep 06 '22 at 13:28
Magic!!! Actually c# by default imports default namespaces in latest versions of the .net framework. It all depends on which version of .net you are using. — AliK, Sep 06 '22 at 13:29
Nice, Nsevens. This is somewhat similar to autoloaded in PHP. — Đạt Phạm Nguyễn Ngọc, Sep 06 '22 at 13:29
No, that's not the same as autoloading in PHP. The latter looks where to find a source file for a given class name. In PHP you still have to type all fully-qualified namespace names for all types you use in a file. — CodeCaster, Sep 06 '22 at 13:31
Nice, Mathias R. Jessen. The site is pretty straightforward to what I'm looking for. — Đạt Phạm Nguyễn Ngọc, Sep 06 '22 at 13:31
It's worth being aware of other brevity-aiding syntax in modern C# too, including expression-bodied members and file-scoped namespaces. Your code is equivalent to this, for example: https://gist.github.com/jskeet/0a07a54f303cc7f796d4a3443ead95de — Jon Skeet, Sep 06 '22 at 13:32
Does using Some.Namespace automatically imports other files in the file structure in C#? Like in PHP, when we want to use some classes from another file, we have to import that file using require_once or in Python, we use the import statement. — Đạt Phạm Nguyễn Ngọc, Sep 06 '22 at 13:46
Thanks, Nsevens. I also find that Microsoft.AspNetCore.Builder also implicitly using. Thanks for the site. — Đạt Phạm Nguyễn Ngọc, Sep 06 '22 at 15:30

score 0 · Answer 1 · answered Sep 06 '22 at 13:33

0

.NET 6 has introduced somthing called implicit global usings. You can read more about it in Scott Hanselman's blog post

https://www.hanselman.com/blog/implicit-usings-in-net-6

answered Sep 06 '22 at 13:33

TWong

91
2
5

Does using Some.Namespace automatically imports other files in the file structure in C#? Like in PHP, when we want to use some classes from another file, we have to import that file using require_once or in Python, we use the import statement. – Đạt Phạm Nguyễn Ngọc Sep 06 '22 at 13:48
In the above example, the using only imports a namespace for usage in that class. It's not a global using. I would direct you to https://stackoverflow.com/questions/9023465/importing-nested-namespaces-automatically-in-c-sharp for a pretty detailed answer. – TWong Sep 07 '22 at 14:27
Just to clarify, global usings only started with .NET 6 (C# 10) - https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-directive. That's probably what you're looking for as someone who's coming over from PHP. – TWong Sep 07 '22 at 15:57

how does C# know what Path class is without giving me have a line 'using System.IO'?

1 Answers1