What does branchAndMerge function in Angular schematics do?

Question

I'm experimenting with Angular schematics, and have encountered the function branchAndMerge() in various places. No one explains what it does, however.

Places I have seen it:

A clarification of how it differs from merge/mergeWith, and how to use it correctly would be appreciated.

P.S: Merge is explained at @angular-devkit/schematics as follows:

Merge the input tree with the other Tree.

Btw I assume that merge() is now mergeWith, though I'm not 100% sure on that.

Code example

const rule = 
    // Creates a new rule that is a concatenation of other rules.
    chain([
      // Everyone uses it, but no one explains what it does...
      branchAndMerge(
        chain([
        // Merges the project tree with the virtual tree
        mergeWith(virtualTree)
      ]))
    ]);

score 2 · Accepted Answer · answered Jul 16 '18 at 01:27

The following video gives the best explanation I've heard of so far:

Branch from current tree, and the tree is a virtual file system based off of your current directory

If one were to look into the code in the repo, one will see this is indeed the case. I would imagine the benefit of doing so, is for performance reasons, wherein it allows one to modify key/values instead of an actual hard disk. In addition, I would imagine it also simplifies process, as it makes the location irrelevant, which can greatly complicate process of schematics.

What does branchAndMerge function in Angular schematics do?

1 Answers1