# `set` action
Assigns values from `.source` to the specified object or session key/path using the specified resolution mode. There are five resolution modes in which the `set` action can operate: [ 'assign', 'defaults', 'defaultsDeep', 'merge', and 'mergeDeep' ].

## Syntax
Using an inline object reference as the target.
```YAML
set:
  mode: assign
  source: 
    { keys/values }
  target: <% object_reference %>
```
Shortcut: using the mode as the action name.
```YAML
merge: # or any of the other resolution modes. # => set: { mode: "assign", ... }
  source: 
    { keys/values }
  target: "key/path"
```
Shorter-cut: default target (session) and using the entire value as the source.
```YAML
assign: 
  { keys/values } # => { source: { keys/value } }
  # target: root of the session 
```

## Properties
### `set.source` property _(required)_
map: The keys/values from the .source object will be set/applied to the target object. If the `set` action value does not have a `.source` property, then the entire value will be used as the `.source` value and the default `.target` will be used.

### `set.target` property
Either a key/path to the session location or an inline object (or <% object_reference %>) for the destination of the key/value assignment. If `set.target` is not specified, then the root of the session will be used.

### `set.mode` property
The resolution mode determines how values are applied if existing values exist. The default mode `assign` will overwrite any values on the target with the new values from `set.source`. Using the mode 'defaults' will cause values to only be set on the target if they did not already exist. 'defaultsDeep' works like 'defaults', except that it recursively descends child objects/properties. 'merge' Will merge values together (including unioning any arrays). 'mergeDeep' applies a merge recursively. For more information about resolution modes and how they work, please see the [lodash](http://lodash.com) documentation for the correspdonding operations.


## Notes
### Note section
Notes about something

## Errors
### ActionStructureError.set
The value of the action must be an object. 

```YAML
set: "value" 
# Raises an ActionStructureError.set
```

## Examples
Setting an array and object as top-level session properties.
```YAML
set:
  fruit: [ apples, bananas, cherries ]
  other_element:
    children: 3
```

```YAML
merge:
  target: json_payload
  value:
```