What's the difference between in-buffer-source and sync-source?

[xuchunyang]

https://github.com/emacs-helm/helm/wiki/Developing#creating-a-source says:

• helm-source-sync, which puts candidates in a list.
• helm-source-in-buffer, which puts candidates in a buffer.

what does it mean for someone who is going to make a new command with helm? what's the advantage that in-buffer source can provide and how to make use of it?

The helm wiki provides two example uses for them, they are achieving the same purpose, so it doesn't help me understand the difference:

(helm-build-sync-source "test"
  :candidates '(a b c d e))

(helm-build-in-buffer-source "test1"
  :data '(a b c d e))

[thierryvolpiatto]

Chunyang Xu <notifications@github.com> writes:

https://github.com/emacs-helm/helm/wiki/Developing#creating-a-source says: + helm-source-sync, which puts candidates in a list. + helm-source-in-buffer, which puts candidates in a buffer. what does it mean for someone who is going to make a new command with helm? what's the advantage that in-buffer source can provide and how to make use of it? The helm wiki provides two example uses for them, they are achieving the same purpose, so it doesn't help me understand the difference: (helm-build-sync-source "test" :candidates '(a b c d e))

Here helm goes in the list generated by :candidates and compares one by one candidates with string-match, when candidate match helm put it in helm-buffer. + Allow modifying list of candidates dynamically while user type in pattern. - Slow.

(helm-build-in-buffer-source "test1" :data '(a b c d e))

Here helm store candidates generated by :data in a special buffer generated with helm-candidate-buffer and search (re-search-forward) in this buffer for candidates matching pattern and put them in helm-buffer. + Much faster. - Support only a fixed list of candidates generated on start. HTH.

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[xuchunyang]

• Allow modifying list of candidates dynamically while user type in
  pattern.

you meant with :volatile t? for example,

(helm :sources
      (helm-build-sync-source "test1"
        :volatile t
        :candidates
        (lambda ()
          (list 1 2 helm-pattern))))

So If I don't need to update the candidate list once it's created, I should use in-buffer source because it is faster, otherwise, I should use sync source.

[thierryvolpiatto]

Chunyang Xu <notifications@github.com> writes:

+ Allow modifying list of candidates dynamically while user type in pattern. you meant with :volatile t?

Yes.

for example, (helm :sources (helm-build-sync-source "test1" :volatile t :candidates (lambda () (list 1 2 helm-pattern)))) So If I don't need to update the candidate list once it's created, I should use in-buffer source because it is faster, otherwise, I should use sync source.

Yes.

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[xuchunyang]

Thanks for your explanation, it is helpful.