Scope. Namespaces

Scope refers to the lifetime and accessibility of a variable. How large the scope is depends on where a variable is declared. For example, if a variable is declared at the top of a class then it will accessible to all of the class methods. If it’s declared in a method then it can only be used in that method.

A pair of curly braces ({}) defines a new scope.

For example:

int Foo {
    int a = 10;
}
int a = 5;
log.message("Foo::a is %d, a is %d", Foo::a,a);

// Output: Foo::a is 10, a is 5

If there is recursion, then variables will be stored in a stack.

int foo(int n) {
	if(n < 2) return 1;
	return foo(n - 2) + foo(n - 1);
}
int n=5;
log.message("%d\n",foo(n));

// Output: 8

Namespaces allow to group entities like classes, objects and functions under a name. This way the global scope can be divided in "sub-scopes", each one with its own name.

The format of namespaces is:

namespace identifier {
	// entities
}

The example of namespace defining:

namespace Foo {
	int a = 10;
}
int a = 5;
log.message("Foo::a is %d, a is %d", Foo::a,a);

// Output: Foo::a is 10, a is 5

It is also possible to use using keyword to introduce a name from a namespace into the current declarative region.

namespace Foo::Bar {
	int a = 10;
}

void foo() {
	using Foo::Bar;
	log.message("Foo::Bar::a is %d\n",a);
}
foo();

// Output: Foo::Bar::a is 10