# Keywords

## Access Keywords

### `base`

The `base` keyword is used to access members of the base class from within a derived class.

* Call a method on the base class that has been overridden by another method.

<pre class="language-csharp"><code class="lang-csharp">public class Person {
    protected string ssn = "444-55-6666";
    protected string name = "John L. Malgraine";
    public virtual void GetInfo() {
        Console.WriteLine("Name: {0}", name);
        Console.WriteLine("SSN: {0}", ssn);
    }
}

class Employee : Person {
    public string id = "ABC567EFG";
    public override void GetInfo() {
        // calling the base class GetInfo() method
<strong>        base.GetInfo();
</strong>        Console.WriteLine("Employee ID: {0}", id);
    }
}

class TestClass {
    static void Main() {
        Employee E = new Employee();
        E.GetInfo();
    }
}

/*
Output
Name: John L. Malgraine
SSN: 444-55-6666
Employee ID: ABC567EFG
*/
</code></pre>

* Specify which base-class constructor should be called when creating instances of the derived class.

<pre class="language-csharp"><code class="lang-csharp">public class BaseClass {
    int num;
    public BaseClass(){
        Console.WriteLine("in BaseClass()");
    }

    public BaseClass(int i) {
        num = i;
        Console.WriteLine("in BaseClass(int i)");
    }
}

public class DerivedClass : BaseClass {
    // This constructor will call BaseClass.BaseClass()
<strong>    public DerivedClass() : base() { }
</strong>
    // This constructor will call BaseClass.BaseClass(int i)
<strong>    public DerivedClass(int i) : base(i) { }
</strong>
    static void Main() {
        DerivedClass md = new DerivedClass();
        DerivedClass md1 = new DerivedClass(1);
    }
}
/*
Output:
in BaseClass()
in BaseClass(int i)
*/
</code></pre>

{% hint style="info" %}
It is an error to use the `base` keyword from within a static method.
{% endhint %}

## Contextual Keywords

### `partial`

Partial type definitions allow for the definition of a class, struct, interface, or record to be split into multiple files.

<pre class="language-csharp"><code class="lang-csharp">namespace PC
{
<strong>    partial class A
</strong>    {
        int num = 0;
        void MethodA() { }
        partial void MethodC();
    }
    
<strong>    partial class A
</strong>    {
        void MethodB() { }
        partial void MethodC() { }
    }
}
</code></pre>

All the parts must use the `partial` keyword, and must have the same accessibility, such as `public`, `private`, and so on. All the parts must be available at compile time to form the final type.

{% hint style="warning" %}
The `partial` keyword isn't allowed on constructors, finalizers, overloaded operators, property declarations, or event declarations.
{% endhint %}


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