# Grid

The trait `Grid`

represents rectangular grids that contain elements of a particular
kind. Each element in a grid is located at a unique pair of coordinates, represented
as a GridPos.

X coordinates run from 0 to `width-1`

, y coordinates from 0 to `height-1`

.
(0,0) corresponds to the upper left corner of the grid.

There are different kinds of grids: the type of element that a grid contains is
defined by the grid’s type parameter. For instance, `Grid[Square]`

is a grid where
each pair of x and y coordinates contains a `Square`

object, and `Grid[House]`

is
a grid containing `House`

objects.

A `Grid`

is mutable: it is possible to replace an element at a particular `GridPos`

with another. (Depending on the element type, the elements may be individually
mutable, too.) The width and height of a grid never change, however.

Upon creation, a `Grid`

initializes itself by calling initialElements, which
produces an initial state for the grid.

This trait has an alias in the top-level package o1, so it’s accessible to students
simply via `import o1.*`

.

- Value parameters:
- height
the number of elements in each column of the grid

- width
the number of elements in each row of the grid

## Value members

### Abstract methods

Generates the elements that initially occupy the grid. This method is automatically
invoked by every `Grid`

object upon creation. Subtypes should implement this method
as appropriate for the particular sort of grid desired.

Generates the elements that initially occupy the grid. This method is automatically
invoked by every `Grid`

object upon creation. Subtypes should implement this method
as appropriate for the particular sort of grid desired.

Note that since this method produces the `Grid`

’s initial contents, it gets called
during initialization before the `Grid`

actually has any elements as content. Therefore,
subtypes’ implementations of this method must not depend on the state of the new `Grid`

(by calling `neighbors`

or `elementAt`

, for instance) or attempt to modify the `Grid`

(with `update`

, for instance).

This method is meant for initialization purposes only. To access all the elements of
an already-initialized `Grid`

, call allElements instead.

- Returns:
a collection of size

`width`

times`height`

that contains the initial grid elements. The first element in the collection will appear at`GridPos`

(0,0), the second at (1,0), and so on, filling in the first row before continuing on the second row at (0,1).

### Concrete methods

Returns a collection of all the elements currently in the grid.

Returns a collection of all the elements currently in the grid.

Returns a collection of all the locations on the grid.

Returns a collection of all the locations on the grid.

Returns the element at the given pair of coordinates. (This does the same as `elementAt`

.)

Returns the element at the given pair of coordinates. (This does the same as `elementAt`

.)

- Value parameters:
- location
a location on the grid (which must be within range or this method will fail with an error)

Determines whether the grid contains the given pair of coordinates. For instance, a grid with a width and height of 5 will contain (0, 0) and (4, 4) but not (-1, -1), (4, 5) or (5, 4).

Determines whether the grid contains the given pair of coordinates. For instance, a grid with a width and height of 5 will contain (0, 0) and (4, 4) but not (-1, -1), (4, 5) or (5, 4).

Returns the element at the given pair of coordinates. (This does the same as `apply`

.)

Returns the element at the given pair of coordinates. (This does the same as `apply`

.)

- Value parameters:
- location
a location on the grid (which must be within range or this method will fail with an error)

Returns a vector of all the neighboring elements of the element indicated by the first parameter. Depending on the second parameter, either only the four neighbors in cardinal compass directions (north, east, south, west) are considered, or the four diagonals as well.

Returns a vector of all the neighboring elements of the element indicated by the first parameter. Depending on the second parameter, either only the four neighbors in cardinal compass directions (north, east, south, west) are considered, or the four diagonals as well.

Note that an element at the grid’s edge has fewer neighbors than one in the middle. For instance, the element at (0, 0) of a 5-by-5 grid has only three neighbors, diagonals included.

- Value parameters:
- includeDiagonals
`true`

if diagonal neighbors also count (resulting in up to eight neighbors),`false`

if only cardinal directions count (resulting in up to four)- middleLoc
the location between the neighbors

Swaps the elements at two given locations on the grid. The given locations must be within range or this method will fail with an error.

Swaps the elements at two given locations on the grid. The given locations must be within range or this method will fail with an error.

Modifies the grid by replacing the existing element at the given location with the new element.

Modifies the grid by replacing the existing element at the given location with the new element.

- Value parameters:
- location
a location on the grid (which must be within range or this method will fail with an error)

- newElement
the new element that replaces the old one at

`location`