A namespace groups related types under a name, such as MyCompany.DataAccess, so two types can share a name without clashing.
Namespaces are hierarchical. That lets you organize a codebase by area and keeps type names short and readable. Code refers to a type by its full name, or imports the namespace with a using directive.
namespace MyCompany.DataAccess
{
public class DatabaseConnection { }
}
namespace MyCompany.UI
{
public class DatabaseConnection { } // Same name, different namespace
}
Namespaces only affect names. They do not control loading, because the runtime loads code by assembly, and one assembly can hold many namespaces.
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One assembly file, many namespaces
Shared.dllthe file the runtime loads
MyCompany.DataAccessa namespace, only part of a type's name
DatabaseConnectionfull name MyCompany.DataAccess.DatabaseConnection
MyCompany.UIa second namespace in the same file
DatabaseConnectionfull name MyCompany.UI.DatabaseConnection
1step
At the top: Shared.dll (the file the runtime loads).
1 / 3← → keys
Shared.dll holds two namespaces, and the same class name lives in each. The runtime loads the file. Namespaces only name its types, and a using directive just shortens names at compile time.
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Interview lens
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Likely follow-ups
How does a namespace differ from an assembly, and can one namespace span several assemblies?A namespace only scopes names. The assembly is the unit the runtime loads and versions, and one namespace can be split across several assemblies.
You import two namespaces that both define DatabaseConnection. How do you resolve the clash?Name the ambiguous reference compile error, then the fixes. Write the fully qualified name, or add a using alias directive such as using Ui = MyCompany.UI;.
Does putting a type in a namespace limit who can use it?No. Access modifiers control visibility. internal limits a type to its assembly, not its namespace, and a namespace takes no access modifier.
How would you structure namespaces in a large multi-project solution?Use the Company.Product.Feature pattern and match the folder layout. Never give a type the same name as its namespace.
What you can say
A namespace groups related types under a name, like MyCompany.DataAccess, so two types can share a short name without clashing.
Namespaces are hierarchical, so I can organize a big codebase by area and still keep type names short and readable.
For example, MyCompany.DataAccess and MyCompany.UI can each have a DatabaseConnection class, and the full names keep the two apart.
In code I either write the fully qualified name or add a using directive for the namespace and use the short name.
Namespaces only affect names, though, because the runtime loads code by assembly and one assembly can hold many namespaces.
Weak answers to avoid
Confuses namespaces with assembliesA namespace is not a DLL and does not control loading. It only scopes names. The runtime loads code by assembly, and one assembly can hold many namespaces.
Says a using directive loads the codeA using directive only lets you write short names. The project still needs a reference to the assembly that has the type, or the build fails.
Treats namespaces as access controlNamespaces hide nothing. Access modifiers set visibility, and internal means the same assembly, not the same namespace.
Defines the term with no clash exampleSaying 'it groups related types' skips why it matters. Show two types with the same name in different namespaces and how code picks the right one.
Interview lens
Likely follow-ups, what you can say, and the weak answers to avoid.
