## Matlab .empty array initialization

Many coding languages have objects that are useful as sentinels to indicate missing data or unused parameters.
For example, if a boolean parameter’s state has not been checked, it’s a bit disingenuous to say `available = false`

.
Sentinel values give a sort of third state that can communicate that something is unknown or unset.

Some example sentinels:

In Matlab an empty array can be used as a sentinel.

## Create Matlab empty arrays

An empty array for a particular Matlab data type is create by appending `.empty`

to the data type name. Examples:

```
datetime.empty
string.empty
struct.empty
```

Then, the commonly used `isempty()`

test works for any Matlab type.

```
function out = myfun(cfg)
arguments
cfg struct = struct.empty
end
if isempty(cfg)
cfg.lims = [0,100];
cfg.out_dir = "~";
end
# ...
```