# `Feel.Value.YearsAndMonthsDuration`
[🔗](https://github.com/FeeJai/BDM/blob/feel-v0.1.0/apps/feel/lib/feel/value/years_and_months_duration.ex#L1)

The FEEL type `years and months duration` (DMN 1.6, section 10.3.2.3.8).

A whole number of months, positive or negative. A month has no fixed length in
seconds, so this type never mixes with `days and time duration`: the two have
no common supertype and are not comparable, except that zero-length durations
of both kinds are equal in one section of the specification.

The components FEEL exposes (`years`, and `months` from 0 to 11) are computed
from the total when read; they are not stored.

## Fields

  * `:months` - the total number of months, an integer.

# `t`

```elixir
@type t() :: %Feel.Value.YearsAndMonthsDuration{months: integer()}
```

# `new`

```elixir
@spec new(integer()) :: t()
```

Builds a duration from a total number of months.

    iex> Feel.Value.YearsAndMonthsDuration.new(13)
    %Feel.Value.YearsAndMonthsDuration{months: 13}

# `parse`

```elixir
@spec parse(String.t()) :: {:ok, t()} | :error
```

Parses a duration string of years and months, as `duration("...")` and `@"..."` read
it: the lexical space of the XPath `yearMonthDuration` (DMN 1.6, section 10.3.4.1).

It is `P`, then years (`nY`), months (`nM`), or both, in that order, with a leading
`-` for a negative duration. The months are not limited to 11: `P26M` is `P2Y2M`.
White space around the string is ignored. Returns `:error` for anything else, which
includes a string with days or a time part (`P1Y2DT3H`: that is not a years and months
duration), a bare `P`, and a number of months beyond 34 digits.

    iex> Feel.Value.YearsAndMonthsDuration.parse("P1Y8M")
    {:ok, %Feel.Value.YearsAndMonthsDuration{months: 20}}
    iex> Feel.Value.YearsAndMonthsDuration.parse("P26M")
    {:ok, %Feel.Value.YearsAndMonthsDuration{months: 26}}
    iex> Feel.Value.YearsAndMonthsDuration.parse("-P1Y")
    {:ok, %Feel.Value.YearsAndMonthsDuration{months: -12}}
    iex> Feel.Value.YearsAndMonthsDuration.parse("P1D")
    :error
    iex> Feel.Value.YearsAndMonthsDuration.parse("P")
    :error

# `type`

```elixir
@spec type() :: Feel.Type.t()
```

Returns the type descriptor of `years and months duration`.

# `value?`

```elixir
@spec value?(term()) :: boolean()
```

Returns `true` for a `t:t/0` with an integer number of months.

---

*Consult [api-reference.md](api-reference.md) for complete listing*