Use Dagger `Qualifier` instead of `Named`

Problem

Currently, we are using Named annotation to define dependencies that have same return types.

@Provides
@Named("full_date")
fun provideDateFormatterForFullDate(locale: Locale): DateTimeFormatter = DateTimeFormatter.ofPattern("d-MMM-yyyy", locale)

@Provides
@Named("date_for_user_input")
fun provideDateFormatterForUserInput(locale: Locale): DateTimeFormatter = DateTimeFormatter.ofPattern("dd/MM/yyyy", locale)

This is problematic because it is not type-safe, a developer can find the issue once they build the project.

Proposal 1

We can define Qualifiers for the different dependencies and use those.

@Qualifier
@Retention(AnnotationRetention.SOURCE)
annotation class FullDate

Then while providing & injecting the dependencies we can Qualifier instead of Named

@Provides
@FullDate
fun provideDateFormatterForFullDate(locale: Locale): DateTimeFormatter = DateTimeFormatter.ofPattern("d-MMM-yyyy", locale)

@field:[Inject FullDate]
lateinit var dateFormatter: DateTimeFormatter

This will allow us to be more type-safe when providing and injecting our dependencies. There is no additional overhead, Named itself is a Qualifier so they both behave the same way.

Problems

• With this approach, we have to define Qualifier for every dependency. I feel like this will increase the amount of code we have to maintain.

Proposal 2

While proposal 1 is the preferred approach, I can understand that we have to define new annotations every time there is a new dependency with the same return type as an already defined dependency. So the easiest approach to make sure using @Named is safe is to define a variable inside Object with the name of the dependency to make sure it’s same across all usages.

object DepsNames {
  const val FULL_DATE = "full_date"
}

@Provides
@Named(FULL_DATE)
fun provideDateFormatterForFullDate(locale: Locale): DateTimeFormatter = DateTimeFormatter.ofPattern("d-MMM-yyyy", locale)

So, what does everyone think? Is it something we should look into? Any other ideas?

[imran0101]

Qualifier Proposal +1

[msasikanth]

I kind of like the qualifier approach since we are removing the usage of primitives and adding information via a type itself. Maintaining a bunch of different annotations isn’t that much overhead over maintaining a list of constants, IMO. In addition the qualifiers are compile time only (correct me if I am wrong here) so it won’t have any impact on our build.

Yes, it will behave the same way Named behaves so it should not affect our builds anymore than Named.