I have been using DateTime and NaiveDateTime alot over the last year and
have found that using the compare function to involves some mental
gymnastics. When using compare you often just want the most recent or
oldest timestamp, or else you want to sort a list of timestamps.
I am proposing four new functions for each module: earliest/2, latest/2,
sort_earliest/2, and sort_latest/2. earliest/2 and latest/2 each take two
DateTime structs and return the first/last time respectively. The
sort_earliest/2 and sort_latest/2 functions take a list and an optional
mapper, similar to the Enum.sort_by/2 function. sort_earliest/2 and
sort_latest/2 will return the list in ascending/descending chronological
order respectively.
Example usage:
```
start_time = DateTime.earliest(datetime1, datetime2)
start_time = Enum.reduce(datetime_list, &DateTime.earliest/2)
sorted_times = DateTime.sort_earliest(datetime_list)
sorted_records = DateTime.sort_earliest(records, &(&1.timestamp))
```
This example is a function that uses sort_earliest to check if a time is
inside a given time range:
```
def in_range(time_stamp, {start_time, end_time} = _range) do
case sort_earliest([time_stamp, start_time, end_time]) do
[^start_time, ^time_stamp, ^end_time] ->
true
_ ->
false
end
end
```
The implementation would be something simple like this:
```
def sort_earliest(list, mapper \\ fn x -> x end) do
Enum.sort_by(list, mapper, fn x, y ->
:lt == DateTime.compare(x, y)
end)
end
def earliest(%DateTime{} = datetime1, %DateTime{} = datetime2) do
case DateTime.compare(datetime1, datetime2) do
:gt ->
datetime2
_ ->
datetime1
end
end
```
Might need to make sure sort_earliest is an in place sort.
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