Shape Area in Go

You write the common part of three shapes, and each shape's area.

Go has no abstract classes. As in the abstract-classes lesson, an interface plays that role. The interface Shape lists two methods:

• area() int returns the shape's area.
• name() string returns the shape's name.

Go interfaces have no method bodies. So the shared part is a function, describe(s Shape). It returns a text such as Square with area 25. That is the name, then with area, then the area.

Three structs are shapes:

• NewRectangle(width, height) builds a Rectangle. Its area is width × height.
• NewSquare(side) builds a Square. Its area is side × side.
• NewRightTriangle(a, b) builds a RightTriangle. Its sides a and b meet at a right angle. Its area is a × b / 2, rounded down.

Their constructors and name() methods are already written. You write each area().

For each shape, the harness prints describe(shape) on its own line.

Example 1:

Input: NewRectangle(3, 4), NewSquare(5), NewRightTriangle(3, 4)
Output:
Rectangle with area 12
Square with area 25
Right triangle with area 6

Explanation: 3 × 4 = 12 and 5 × 5 = 25.
The triangle is half of 3 × 4, so 6.

Example 2:

Input: NewRightTriangle(3, 5), NewSquare(1)
Output:
Right triangle with area 7
Square with area 1

Explanation: Half of 3 × 5 is 7.5.
It rounds down to 7.

Example 3:

Input: NewRectangle(1, 7), NewRightTriangle(1, 1)
Output:
Rectangle with area 7
Right triangle with area 0

Explanation: A 1 by 7 rectangle has area 7.
Half of 1 × 1 rounds down to 0.

Constraints:

• 1 to 100 shapes.
• Each size is a whole number from 1 to 10,000.