[ScopedValue] best way to conditionally bind a value ?

[Alan Bateman]

On 30/07/2025 19:16, Benoit LEFEVRE -CAMPUS- wrote:
> Hello
>
>     After using the ScopedValue for a few days, I'm wondering if there
>     is a better way to conditionally bind a value than doing the
>     following :
>
>
>         public static final ScopedValue< Locale > ACCEPT_LANGUAGE =
>         ScopedValue.newInstance();
>         public static final ScopedValue< String > USER_ID =
>         ScopedValue.newInstance();
>
>         final Locale acceptLanguage = getAcceptLanguageFromHeader(
>         httpRequest );
>
>
>         if( acceptLanguage == null ) {
>             ScopedValue
>                 .where( USER_ID, uid )
>                 .call( MyClass::myStaticCallableMethod );
>         } else {
>             ScopedValue
>                 .where( USER_ID, uid )
>                 .where( ACCEPT_LANGUAGE, acceptLanguage )
>                 .call( MyClass::myStaticCallableMethod );
>         }
>
>
>     The point for me of doing so, instead of simply setting a null
>     acceptLanguage, is to have a more readable code afterward :
>
>
>         private String myStaticCallableMethod() {
>             final Local localToUse = ACCEPT_LANGUAGE.orElse(
>         A_DEFAULT_LOCAL );
>
>
>             ...
>         }
>
>
>     What is your advise about it ?
>

If the user ID and accept language were (explicit) method parameters 
then you might write:

if (acceptLanguage == null) {
     MyClass.myStaticCallableMethod(uid);
} else {
     MyClass.myStaticCallableMethod(uid, acceptLanguage);
}

With implicit method parameters you've got the same if-then-else so I 
don't think it is terrible.

Is there any reason why the caller can't bind ACCEPT_LANGUAGE to 
A_DEFAULT_LOCALE so that the callee doesn't need to handle it? That 
would change the usage to:

ScopedValue
     .where(USER_ID, uid)
     .where(ACCEPT_LANGUAGE, (acceptLanguage != null) ? acceptLanguage : 
A_DEFAULT_LOCALE)
     .call(...);

It would then be a bug f myStaticCallableMethod were called without 
bindings for either.

-Alan

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