Using and namespace

Question

Where to place using System or other namespaces? Which is the correct or the better way to write code and why? According to my c# trainer it is the second, but everywhere I see the first one.

using System;
namespace Program
{
    class SomeClass
    {
    }
}

or

namespace Program
{
using System;

    class SomeClass
    {
    }
}

According to my c# trainer it is the second, but everywhere I see the first one.

Your C# trainer probably has a Java background and doesn't know better... — Thorsten Dittmar, Jan 31 '14 at 12:11
Check this http://stackoverflow.com/questions/11812088/differences-between-using-import-inside-or-outside-of-namespace — slash shogdhe, Jan 31 '14 at 12:12
http://stackoverflow.com/questions/125319/should-usings-be-inside-or-outside-the-namespace — Nagaraj S, Jan 31 '14 at 12:15

score 3 · Accepted Answer · answered Jan 31 '14 at 12:16

The scope of a using directive is limited to the file in which it appears.

Create a using alias to make it easier to qualify an identifier to a namespace or type. The right side of a using alias directive must always be a fully-qualified type regardless of the using directives that come before it.

Create a using directive to use the types in a namespace without having to specify the namespace. A using directive does not give you access to any namespaces that are nested in the namespace you specify.

Refer: http://msdn.microsoft.com/en-us/library/sf0df423.aspx

score 2 · Answer 2 · answered Jan 31 '14 at 12:10

It is your choice. The second can be handy if you have a code file with multiple namespaces, but only want to use a namespace import within one of these namespaces. However, most coding guidelines that I have seen so far specify that a file may only contain one namespace at most and the usings at the top of the file, in alphabetic order.

score 1 · Answer 3 · answered Jan 31 '14 at 12:21

Stylecop by default requires you to put usings inside namespaces - see here; for the following reason: (from linked page):

There are subtle differences between placing using directives within a namespace element, rather than outside of the namespace, including:

Placing using-alias directives within the namespace eliminates compiler confusion between conflicting types.
When multiple namespaces are defined within a single file, placing using directives within the namespace elements scopes references and aliases.

score 0 · Answer 4 · answered Jan 31 '14 at 12:07

0

Using is always on the top of the document.

answered Jan 31 '14 at 12:07

Dieter B

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Why's that? The other way it compiles, too? – Thorsten Dittmar Jan 31 '14 at 12:10
@Devcon this is not a requirement. – Selman Genç Jan 31 '14 at 12:17

Using and namespace

4 Answers4