Component ID's created from object types passed through template in Entity Component System

So I've been learning about Entity Component Systems(ECS) and came across this method for creating unique ID's by passing the object as a template parameter. I was wondering how the line:

 static ComponentID typeID{getUniqueComponentID()};

is creating ID's without having a duplicate ID created again. I know it's probably glaringly obvious.

Here's the entire code that works and doesn't repeat any ID's

#include <iostream>

using ComponentID = std::size_t;

//Creates a unique ID for and component that is created
inline ComponentID getUniqueComponentID() noexcept{

    //states that the static ComponentID is going to start at 1
    static ComponentID lastID{1u};
    std::cout<< "Created ID: " << lastID << std::endl;
    return lastID++;

}

//gets the component ID of the Type that is being passed into template
template<typename T>
inline ComponentID getComponentTypeID() noexcept{

    //ComponentID is tied to the templated object type
    static ComponentID typeID{getUniqueComponentID()};
    return typeID;
}

struct A{};
struct B{};
struct C{};

int main(int argc, const char * argv[]) {

   std::cout << getComponentTypeID<A>() << std::endl;
   std::cout << getComponentTypeID<B>() << std::endl;
   std::cout << getComponentTypeID<C>() << std::endl;
   std::cout << getComponentTypeID<C>() << std::endl;
   /*
   Output:
   1
   2
   3
   3
   */

   return 0;
}