Settings nodes merging

Merge is the operation of reducing two settings nodes to one: left + right --> result.

Its primary use is to combine configuration sources.

API

Each node type implements a Merge method that accept another node (right in our terms) and an instance of merge options with following properties:

Property	Values	Description
ObjectMergeStyle	Deep, Shallow	Type of the merge procedure performed on object nodes. Deep is the default style.
ArrayMergeStyle	Replace, Concat, Union, PerElement	Type of the merge procedure performed on array nodes. Replace is the default style.

SettingsNodeMerger is a handy public helper used to merge arbitrary nodes that handles nulls:

var result = SettingsNodeMerger.Merge(left, right, SettingsMergeOptions.Default);

General merging rules

• If both nodes are null, the result is also null.

• If one of the nodes is null, the non-null node wins:

  • left + null --> left

  • null + right --> right

• If nodes are of different types, the right node always wins:

  • value + array --> array

  • array + object --> object

  • object + value --> value

• If nodes are of same type, special rules apply. They are described in the next sections.

Merging two value nodes

Right node always wins: left value + right value --> right value.

Merging two array nodes

Replace style (default) always preserves the right array:

left array + right array --> right array.

Concat style produces an array containing elements from both arrays. All elements from the left array, then all elements from the second one, preserving order inside arrays.

[1, 2] + [2, 3] --> [1, 2, 2, 3]

Union style produces an array containing unique items from both arrays. The order is the same to Concat style.

[1, 2, 3] + [2, 3, 4] --> [1, 2, 3, 4]

Per element style produces an array containing items obtained by merging corresponding items (by index) from both arrays. If merged arrays have different children count, the "tail" of the longer array is preserved as-is.

[1, 2, 6] + [4, 5] --> [4, 5, 6]

Merging two object nodes

Deep style (default) produces an object with union of the children from both nodes, then merges children with same names recursively.

{A:1} + {B:2} --> {A:1, B:2}

{A: {C:1}, B: {D:2}} + {A: {E:3}, B: {F:4}} --> {A: {C:1, E:3}, B: {D:2, F:4}}

Shallow style compares children of both nodes by names. If the sets of names match, regardless of order, merges the pairs of matching children recursively. Elsewise, just prefers to return the right node.

{A:1} + {B:2} --> {B:2}

{A:1} + {A:2} --> {A:2}

Related pages

Settings nodes

Combine sources