Namespaces

Namespace Alias

// Use type name "json" instead of "nlohmann::json"
using json = nlohmann::json;

Global Namespace

A :: with nothing in front of it means starting at the global namespace.

// Google Test example:
class MyClassTest : public ::testing::Test {
};

Nested Namespaces

A child namespace has access to everything in its parent/ancestor namespaces.

my::parent {

class ParentNameClass {
};

}

my::parent::child {

ParentNameClass parent_instance;

}

From StackOverflow:

Simplified basic C++ namespace rules are:

• You can access anything in parent namespace path without specifying namespace.

• You can access anything in child namespace path by specifying only relative path.

• Everything else requires full namespace specifications.

"using" Keyword

Bring in a specific object from a different namespace, so you can refer to it directly.

using my::space::MyClass;
// You can now refer to MyClass directly by name
// instead of using the full namespace prefix.

Bring in an entire namespace.

using namespace std;
// You can now use anything from the `std` namespace
// directly by name without using the `std::` prefix.