<a id="nupp.mem.indexed"></a>
# `nupp.mem.indexed`

One inclusive range, checked once against every view a loop is about to index.

A loop that walks two views together needs the same bounds to hold for both, and
checking them separately checks them twice and says nothing about the pair.
`range` takes the views and answers bounds that are valid for all of them.

```nupp
local indexed = nupp.mem.indexed

const bounds = indexed.range(1, 4, left, right)
for i = bounds.first, bounds.last do
    print(left[i], right[i])
end
```

The checker validates the variadic operands against their trusted descriptors,
so only a sealed view contract can be passed. The runtime body stays
representation-neutral and reads the private count slot each bundled view
implementation carries.

See `nupp.mem.span` for the views this validates, and
[ownership.md](../../../../learn/runtime/ownership/borrowing/index.html) for the borrow rules they are written against.

## Types

<a id="nupp.mem.indexed.Range"></a>
### `Range` _record_

```nupp
record indexed.Range
    readonly first: integer
    readonly last: integer
end
```

Inclusive integer bounds validated once against every supplied indexed view.

#### Fields

<a id="nupp.mem.indexed.Range.first"></a>
##### `first`

```nupp
first: integer
```

The one-based first index, inclusive.

<a id="nupp.mem.indexed.Range.last"></a>
##### `last`

```nupp
last: integer
```

The one-based last index, inclusive. One below `first` is an empty range.

## Functions

<a id="nupp.mem.indexed.range"></a>
### `indexed.range` _function_

```nupp
function indexed.range(first: integer, last: integer, borrows ?: any): indexed.Range
```

Validates one inclusive range against every view supplied after it.

At least one view is required: bounds nothing was checked against are not
bounds. The views are borrowed for the call, so this may be written inline in
the `for` header that uses the result.

```nupp
const bounds = indexed.range(1, 4, left, right)
for i = bounds.first, bounds.last do
    print(left[i], right[i])
end
```

#### Arguments

| Name | Type | Description |
| --- | --- | --- |
| `first` | `integer` | the one-based first index, inclusive |
| `last` | `integer` | the one-based last index, inclusive |
| `borrows ...` | `any` |  |

#### Returns

| Type | Description |
| --- | --- |
| `indexed.Range` | the validated bounds |

#### Raises

- when no view is supplied or the bounds exceed a supplied view