telemere/main/resources/signal-docstrings/log!.txt
Peter Taoussanis ac5feb4723 [mod] [#53] Breaking: change return value of log!, event!
This change will only affect rare advanced users that depend on
the return value of `log!` or `event!`. For all other users this
will be a non-breaking change.

Before this commit:
  `log!` and `event!` returned true iff signal was allowed.

After this commit:
  `log!`  and `event!` now ALWAYS return nil.
  `log!?` and `event!?` have been added that keep the old behaviour.

Motivation:
  It's pretty rare to use the return value when generating log or event
  signals. I originally included the return value since it CAN be handy,
  and I figured it could just be ignored by those that don't need it.

  But #53 showed that there's a downside I hadn't anticipated - some
  users may actually depend on / prefer a nil return to prevent
  accidentally affecting program flow.

  I think that's a legitimate enough concern to still make a change now
  before v1 final.

  Apologies for the nuissance!
2025-03-03 11:19:36 +01:00

38 lines
1.4 KiB
Text

"Log" signal creator, emphasizing (optional level) + message.
Default kind: `:log`
Default level: `:info`
Returns:
- For `log!` variant: nil, unconditionally.
- For `log!?` variant: true iff signal was created (allowed by filtering).
When filtering conditions are met [4], creates a Telemere signal [3] and
dispatches it to registered handlers for processing (e.g. writing to
console/file/queue/db, etc.).
Examples:
(log! "My msg") ; %> {:kind :log, :level :info, :id ::my-id ...}
(log! :warn "My msg") ; %> {... :level :warn ...}
(log!
{:let [x "x"] ; Available to `:data` and `:msg`
:data {:x x}}
["My msg:" x]) ; %> {... :data {x "x"}, :msg_ "My msg: x" ...}
Tips:
- Test using `with-signal`: (with-signal (log! ...)).
- Supports the same options [2] as other signals [1].
- `log!` and `event!` are both good default/general-purpose signal creators.
- `log!` emphasizes messages, while `event!` emphasizes ids.
- `msg` arg may be a string, or vector of strings to join with `\space`.
- See also `msg-splice`, `msg-skip` utils.
----------------------------------------------------------------------
[1] See `help:signal-creators` - (`signal!`, `log!`, `event!`, ...)
[2] See `help:signal-options` - {:keys [kind level id data ...]}
[3] See `help:signal-content` - {:keys [kind level id data ...]}
[4] See `help:signal-filters` - (by ns/kind/id/level, sampling, etc.)