Scope. Namespaces

Scope is a region of a program that determines accessibility of an identifier (whether a variable, enum, function, class, namespace and so on) that is used in this program.

How large the scope is depends on where the identifier is declared. For example, if a variable is declared at the top of a class then it will be 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:

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

Foo::a is 10, a is 5

If an identifier is declared outside all blocks enclosed by curly braces, it will have the global scope. It means that such identifier will be accessible anywhere in the program after its declaration.

// function foo() is in the global scope
int foo() { log.message("Function in the global scope\n"); }

class Foo {
    Foo (){}
    // function foo() is in the scope of class Foo
    int foo(){ log.message("Class member function\n"); }
};

As it was mentioned above, lifetime of a variable is not limited by a current scope. In other words, lifetime of local variables is the same as lifetime of global ones (unless otherwise specified). For example:

int foo() {
    int local_var;
    local_var++;
    log.message("local_var: %d\n",local_var);
}

foo(); // local_var: 1
foo(); // local_var: 2

If you want to emulate local lifetime of the local_var variable, it should be initialized as follows:

int foo() {
    int local_var = 0;
    local_var++;
    log.message("local_var: %d\n",local_var);
}

foo(); // local_var: 1
foo(); // local_var: 1

Scope Resolution Operator

namespace Test {
    int a;
    void info() { log.message("a from the scope of the 1st namespace is %d\n",a); }
}

int init () {

    namespace Test {
        int a;
        void info() { log.message("a from the scope of the 2nd namespace is %d\n",a); }
    }
	// access to the members of the global namespace 
    ::Test::a = 10;
    ::Test::info();
	
	// access to the members of the namespace declared in the current scope
    Test::a = 30;
    Test::info();

    return 1;
}

a from the scope of the 1st namespace is 10 
a from the scope of the 2nd namespace is 30

class Foo {
    Foo() {}

    // user-defined function in the scope of the Foo class
    void rotate(float angle) {
        // UnigineScript function used to get a matrix of rotation at the given angle around the axis
        mat4 rot = ::rotate(vec3(1.0f, 0.0f, 0.0f), angle);
    }
};

NameSpace::getFunctionID(): can't find "rotate" function with 2 arguments

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