# Type Modification

A field may be used to generate other instances of `Field`. This can
be convenient to alter the type or name of a field. Since `Field` is
immutable, it simply generates another instance.

## Index

When defining indexes, MongoDB lets define ascending or descending
order, hence the same field name is used as a key, but value is `Int`
regardless of the original type it has. So, `Field[T]` has method
`int` to quickly create a `Field[Int]` with the same name:

```scala
val userName = "uname".fieldOf[String]
collection.ensureIndex(userName.int === 1, userName.int === -1)
```

## Any Field

`Field[Any]` field (created by `any` method) may be helpful to write
or read a field "as is". If you absolutely certain in what you are
doing, 

```scala
collection.modify(userName === "john", userName.any.set(10566))
```

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