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https://issues.apache.org/jira/browse/LOG4J2-599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13964339#comment-13964339
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Nick Williams commented on LOG4J2-599:
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To be clear, {{toString}} of a {{Supplier}} is completely meaningless. It'll
look something like "com.MyClass$lambda$18972349\ou98!uc". If someone provides
a {{Supplier}}, they don't mean for you to call {{toString}} on it.
{{Callable}}, on the other hand, I can see your point. Maybe we only support a
"smart API" for {{Supplier}}?
The problem with a separate API is it actually makes it MORE difficult to use.
What if MOST of my arguments are simple, but ONE of them needs to be evaluated
on a deferred basis? Consider this:
{code:java}logger.trace("Enter {} {} {} {}", argument1, argument2, (Supplier)()
-> argument3.someMethod(), argument4);{code}
Having a separate Supplier API would make this impossible. They'd have to use a
lambda for all four arguments.
> Support lambda functions (or similar) for log message parameters
> ----------------------------------------------------------------
>
> Key: LOG4J2-599
> URL: https://issues.apache.org/jira/browse/LOG4J2-599
> Project: Log4j 2
> Issue Type: Brainstorming
> Components: Core
> Reporter: Matt Sicker
> Priority: Minor
>
> It would be nice if we could support 0-param lambda functions (or the
> equivalent: interfaces with a single empty-parameter message call), or more
> simply, allow Runnables (or something similar) to be passed which will be
> dynamically executed if the log message is enabled.
> The use case here is that although string construction of the log message is
> a performance issue that is already solved quite well, the problem of adding
> in information to the log message that makes other calculations still needs
> to be wrapped in an if check.
> I'm not sure if it'd be best to just use Runnable, or create a new interface,
> or try to emulate how Java 1.8 lambdas work via an interface with a single
> method defined. The details here would still need to be fleshed out, but I
> think this sort of feature could be rather handy (especially in a Java 1.8+
> environment, or in Groovy/Scala/etc.).
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