Скачать или смотреть Efficiently Decoding and Converting String to Double in Swift's Codable

A comprehensive guide on decoding JSON strings to doubles using Swift's Codable, complete with examples and best practices for maintaining flexible code structures.
---
This video is based on the question https://stackoverflow.com/q/62847749/ asked by the user 'n83' ( https://stackoverflow.com/u/1368513/ ) and on the answer https://stackoverflow.com/a/62848509/ provided by the user 'Joakim Danielson' ( https://stackoverflow.com/u/9223839/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Decoding and converting string to double in codable

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Efficiently Decoding and Converting String to Double in Swift's Codable

When working with JSON data in Swift, especially in the context of currency conversion, it's common to encounter issues while decoding JSON strings to numeric types. This post will help you understand how to parse such JSON data using Swift's Codable protocol. We’ll address common pitfalls and offer a cleaner, more maintainable approach using a well-structured model.

The Problem

Consider the following JSON, which represents currency values:

[[See Video to Reveal this Text or Code Snippet]]

Attempting to decode this JSON directly into a struct using Double properties fails due to the fact that the values are provided as strings instead of numbers. This leads to an error similar to the following:

[[See Video to Reveal this Text or Code Snippet]]

This error indicates that the decoder expected a Double, but found a String instead. Hence, a different approach is necessary for correct decoding.

The Solution

To effectively parse this JSON data, we will create a flexible structure that can handle various currency rates without causing type mismatches. Here's how to do it:

Step 1: Create a CurrencyRate Struct

Instead of directly associating currencies with Double values in your existing struct, we'll define a new struct, CurrencyRate, which will hold the currency type and its corresponding rate.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Decode the JSON as a Dictionary

Instead of attempting to decode the JSON directly into a model with Double, we can decode it first into a dictionary of [String: String]. This serves as an intermediary representation of our data.

[[See Video to Reveal this Text or Code Snippet]]

Why This Approach Works

Flexible Structuring: This new method allows adding more currency types easily without modifying the core structure.

Decimal Precision: Using Decimal instead of Double helps avoid precision issues common with floating-point arithmetic, especially crucial when dealing with currency values.

Important Considerations

Assumptions on Currencies: Depending on your use case, you might want to include a base currency or other relevant properties in your CurrencyRate struct to better categorize or manage your currency data.

Creating a Currency Type: If needed, creating a type for currency properties, such as Currency, could add clarity and type safety to your code base.

Conclusion

In conclusion, converting JSON strings to numeric types in Swift requires careful structuring to avoid common pitfalls like type mismatches. By utilizing the Codable protocol along with a dictionary-based approach, we can establish a flexible model that accommodates various currency rates. This not only resolves the decoding error but also future-proofs your code against potential expansions.

By following the guidelines provided in this post, you can ensure that your application handles currency data with accuracy and efficiency.