How to Call Functions from Generic Functions in Kotlin Without Knowing the Type

Описание: Discover techniques to call functions from generic functions in Kotlin effectively, even without type knowledge. Learn about using ConverterRegistry for flexible type conversions!
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This video is based on the question https://stackoverflow.com/q/64719513/ asked by the user 'Dalibor Filus' ( https://stackoverflow.com/u/737956/ ) and on the answer https://stackoverflow.com/a/64748461/ provided by the user 'Adam Arold' ( https://stackoverflow.com/u/485337/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Call Functions from Generic Functions in Kotlin Without Knowing the Type

In the world of Kotlin programming, one common challenge developers face is calling a specific function from a generic function without having prior knowledge of the type involved. This scenario is even more complex when dealing with multiple classes and their corresponding data transfer objects (DTOs). If you've encountered this issue in your coding endeavors, you're not alone. Let's dive into this problem and uncover the solutions available to you.

Understanding the Challenge

Consider the following situation: You have two entities (Someotherthing and Something) and their respective DTOs (SomeotherthingDTO and SomethingDTO). You also have a convert function designed to transform an entity into its DTO. However, when you attempt to create a generic function intended to handle this conversion, you'll realize that the function will raise errors due to not knowing which specific convert function to call based on the supplied entity type.

Here’s a quick look at the problematic code:

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Attempting to call this generic function may lead to compiler errors indicating that none of the existing convert functions can be invoked with the argument you provided.

The Solution: Utilizing a Converter Registry

Currently, a proposed solution relies on using a Converter interface alongside a ConverterRegistry. This allows us to define conversion pairs explicitly and dynamically handle conversions based on the classes involved. Let's break down how this works.

Step 1: Define the Converter Interface

The first step is to create an interface that represents a converter:

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Here, we define:

fromClass: The source class type.

toClass: The destination class type.

convert: The method to convert from the source to the destination type.

Step 2: Create a ConverterRegistry

Next, we create a registry to manage our converters:

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This registry can attempt to find an appropriate converter based on the type classes provided at runtime.

Step 3: Implement the Converters and Registry

When setting up your registry, you will need to register the available converters:

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This registry will search through the registered converters and attempt to convert the input types as needed.

Conclusion

While Kotlin currently lacks direct support for reflection-enabled type conversion in generics, utilizing a ConverterRegistry serves as an effective workaround. By defining converters and managing them within a registry, you gain flexibility and can dynamically handle various type conversions without knowing the specifics of the entities in advance.

Next time you are confronted with the challenge of calling functions from a generic function without type knowledge, remember these strategies. They’ll make your Kotlin programming experience smoother and more efficient!