How to extend float3 or any other built-in type to conform to the Codable protocol?

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05-09-2024

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Conforming float3 (and other Built-in Types) to the Codable Protocol in Swift

The float3 type, along with other built-in types in Swift, doesn't inherently conform to the Codable protocol. This means you can't directly encode or decode them using JSONEncoder or JSONDecoder without some extra work. This article will explore how to extend these built-in types to make them Codable.

Understanding the Challenge:

The issue with the original code snippet lies in the fact that float3 isn't a basic type like Int or Float. It's a structure containing three Float values (x, y, and z) and additional functionality for vector operations. This structure doesn't automatically map to a JSON format, so you need to explicitly define how it should be encoded and decoded.

The Solution: Custom Encoding and Decoding

The solution lies in creating an extension for the float3 struct that implements the Codable protocol:

import SceneKit

extension float3: Codable {
    public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let values = try container.decode([Float].self)
        guard values.count == 3 else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid float3 data")
        }
        self = float3(values[0], values[1], values[2])
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode([x, y, z])
    }
}

Explanation:

1. init(from decoder: Decoder): This initializer handles decoding.

   • It uses decoder.singleValueContainer() because we want to decode a single array of floats representing the float3 vector.
   • It then attempts to decode the array of Float values.
   • It verifies that the array has exactly three elements to ensure valid data.
   • Finally, it initializes the float3 instance using the decoded Float values.

2. encode(to encoder: Encoder): This method handles encoding.

   • It creates a singleValueContainer to encode the float3 as a single JSON array.
   • It then encodes the x, y, and z values as an array of Float.

Using the Extension:

Now that float3 conforms to Codable, you can encode and decode it:

let float3Instance = float3(1.0, 2.0, 3.0)

let encoder = JSONEncoder()
let encodedData = try encoder.encode(float3Instance)

let decoder = JSONDecoder()
let decodedInstance = try decoder.decode(float3.self, from: encodedData)

print(decodedInstance) // Output: float3(x: 1.0, y: 2.0, z: 3.0)

Generalizing for other Built-in Types:

This approach can be applied to other built-in types like float4, double2, etc. Simply adjust the number of elements in the [Float] array to match the type's component count.

Key Takeaways:

• You can customize the encoding and decoding process for built-in types by making them conform to the Codable protocol.
• The singleValueContainer is often useful for encoding or decoding simple structures that map to a single JSON value.
• Data validation during decoding is crucial to ensure data integrity.

Further Considerations:

• Performance: For frequent encoding/decoding operations, consider optimizing the implementation for better performance.
• Custom Naming: You can customize the JSON key names using the CodingKeys enum if needed.

By understanding how to extend built-in types, you gain greater control over how they are encoded and decoded, making your code more flexible and efficient.