StringTemplates deferred evaluation

[Anatoly Kupriyanov]

Classically (how it was done a decade or so ago) the logger method would
look like:
void debug(String template, Object arg1, Object arg2) {
  if(!enabled) return;
  writeLog(interpolate(template, arg1.toString(), arg2.toString()));
}

That allows that  if enabled==false, then it will be zero-gc, guaranteed.
It even used a lot of overrides with zero args, one arg, two args to avoid
...-ellipsis array allocation. E.g. see
https://www.slf4j.org/api/org/slf4j/Logger.html

There is a C# hacky approach the String Interpolation Handler (
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/interpolated-string-handler
) to use struct (allocated on stack) and magical isEnabled flags to cover
logging effectively.

I don't see how it would be possible to use the StringTemplate to achieve
the similar effectiveness, unless there are some good and reliable
optimizations in JIT to avoid allocations.

On Sun, 17 Mar 2024 at 16:41, David Alayachew <davidalayachew at gmail.com>
wrote:

> The cost would be no different than evaluating a StringTemplate lazily.
> Utlimately, log.debug(blah) is still a method call, and therefore, some
> object is going into the method. Whether we evaluate the StringTemplate
> lazily or the Supplier<StringTemplate> lazily is largely the same thing.
>
> Or am I misunderstanding you?
>
> On Sun, Mar 17, 2024 at 12:28 PM Anatoly Kupriyanov <kan.izh at gmail.com>
> wrote:
>
>> But the "() ->" thing is still a runtime object to be allocated on the
>> heap... or is the JIT smart enough to always optimize it out?
>>
>> On Sun, 17 Mar 2024 at 16:17, David Alayachew <davidalayachew at gmail.com>
>> wrote:
>>
>>> I feel like that would be on the logging libraries to provide, not so
>>> much the language.
>>>
>>> Let's say that your problem (as I understand it) is like this.
>>>
>>> log.debug("metrics =
>>> \{this.expensiveComputationThatNormallyWouldntRunUnlessYouActivateDebug()}");
>>>
>>> Sounds to me like the solution is this instead.
>>>
>>> log.debug(() -> "metrics =
>>> \{this.expensiveComputationThatNormallyWouldntRunUnlessYouActivateDebug()}"
>>> )
>>>
>>> So, your logging library just needs to add a new overload for a
>>> Supplier<StringTemplate>, and then this problem is solved entirely outside
>>> of the language. Log4J and friends are pretty good about keeping up with
>>> new additions, so it should not take long.
>>>
>>> I know it's a little less convenient, but doing it this way helps keep
>>> out complexity from the feature, and only introduces it where necessary
>>> (and it's only necessary at use-site).
>>>
>>> Would this meet your needs?
>>>
>>> On Sun, Mar 17, 2024 at 11:15 AM Justin Spindler <
>>> justin.spindler at gmail.com> wrote:
>>>
>>>> I was toying around with the second preview of StringTemplates and I
>>>> had a question regarding their design.  I was wondering if it had been
>>>> considered for the embedded expressions to be evaluated lazily?
>>>>
>>>> One of the first use cases that came to mind when I was exploring
>>>> StringTemplates is logging.  That is an extremely common case where we want
>>>> to produce a form of interpolated value, and the current syntax generally
>>>> has the same concerns that a formatted string would, in that the inputs are
>>>> removed from where they are defined within the message format.  However, if
>>>> the log message is below the log level threshold you generally don't want
>>>> to incur the cost of building the message, including evaluating those
>>>> embedded expressions.  Log libraries typically offer a mechanism to defer
>>>> evaluation via Suppliers, but that feels like it would be a challenge to
>>>> use within StringTemplate.
>>>>
>>>> C# is an example of a language that offers this functionality via
>>>> FormattableString, which gives a method the ability to choose whether or
>>>> not to interpret the template or evaluate the expressions.  That allows
>>>> logging below threshold to be more or less a no-op.
>>>>
>>>>
>>>>
>>
>> --
>> WBR, Anatoly.
>>
>

-- 
WBR, Anatoly.
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