# 過載

D程式設計允許為一個函式名或在相同的範圍內操作，這就是所謂的函式過載和運算子過載分別指定一個以上的定義。

## 函式過載

```import std.stdio;
import std.string;
class printData
{
public:
void print(int i) {
writeln("Printing int: ",i);
}

void print(double  f) {
writeln("Printing float: ",f );
}

void print(string s) {
writeln("Printing string: ",s);
}
};

void main()
{
printData pd = new printData();

// Call print to print integer
pd.print(5);
// Call print to print float
pd.print(500.263);
// Call print to print character
pd.print("Hello D");
}```

```Printing int: 5
Printing float: 500.263
Printing string: Hello D
```

## 運算子過載

```Box opAdd(Box b)
{
Box box = new Box();
box.length = this.length + b.length;
box.height = this.height + b.height;
return box;
}```

```import std.stdio;

class Box
{
public:

double getVolume()
{
return length * breadth * height;
}
void setLength( double len )
{
length = len;
}

{
}

void setHeight( double hei )
{
height = hei;
}

{
Box box = new Box();
box.length = this.length + b.length;
box.height = this.height + b.height;
return box;
}
private:
double length;      // Length of a box
double height;      // Height of a box
};
// Main function for the program
void main( )
{
Box box1 = new Box();    // Declare box1 of type Box
Box box2 = new Box();    // Declare box2 of type Box
Box box3 = new Box();    // Declare box3 of type Box
double volume = 0.0;     // Store the volume of a box here

// box 1 specification
box1.setLength(6.0);
box1.setHeight(5.0);

// box 2 specification
box2.setLength(12.0);
box2.setHeight(10.0);

// volume of box 1
volume = box1.getVolume();
writeln("Volume of Box1 : ", volume);

// volume of box 2
volume = box2.getVolume();
writeln("Volume of Box2 : ", volume);

// Add two object as follows:
box3 = box1 + box2;

// volume of box 3
volume = box3.getVolume();
writeln("Volume of Box3 : ", volume);

}
```

```Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400```

S.N. 過載型別
1 一元運算子過載
2 二元運算子過載
3 比較操作符過載