# C++ Instantiable or not
## What does "instantiable" mean in C++
- "Instantiable" means:
> You can create objects (instances) of a class
- Example

    class Dog {
        // ...
    };

    int main() {
        Dog d;  // ✅ "Dog" is instantiable — this creates an instance
    }

- Dog is instantiable because you can write Dog d;
## When does a class not instantiable?
### Abstract class (with pure virtual function)
- A class with at least one pure virtual function is abstract
- You cannot create an object from it directly
- ➡️ But you can derive from it and instantiate the child if it implements the pure virtual function

    class Animal {
    public:
        virtual void makeSound() const = 0;  // pure virtual
    };

    Animal a;  // ❌ Error: Animal is abstract

### Private constructor (singleton pattern, static factory, etc.)

class A {
private:
    A() {}
};

A a;  // ❌ Error: constructor is private

### Deleted constructor

class B {
public:
    B() = delete;
};

B b;  // ❌ Error: constructor is deleted

## Why would you want a class to be not instantiable?
Under conditions when you create a class not to make objects from it, but rather to
- Serve as a base class (abstract interface)
- Provide only static utilities (no object needed)
- Enforce factory or singleton patterns
- Prevent misuse of the class
- Model conceptual entities that don't have a direct object form