Solving the Cannot convert value of type '[String]' to type 'NSString' in coercion Error in Swift

Описание: Are you facing the error "Cannot convert value of type '[String]' to type 'NSString' in coercion" in your Swift code? Learn how to resolve this issue with a proper conversion technique from strings to doubles in Swift.
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This video is based on the question https://stackoverflow.com/q/65002209/ asked by the user 'psettle41' ( https://stackoverflow.com/u/14634650/ ) and on the answer https://stackoverflow.com/a/65002410/ provided by the user 'vadian' ( https://stackoverflow.com/u/5044042/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Cannot Convert Value of Type '[String]' to Type 'NSString' in Coercion Error

If you're new to Swift programming and trying to convert an array of strings into a double value, you may have come across the error message: "Cannot convert value of type '[String]' to type 'NSString' in coercion." This error indicates that you're attempting to coerce an array ([String]) into a single string (NSString). Let's examine the problem and how to solve it effectively.

The Problem

In the given code snippet, you've defined an array of latitude string values and are trying to convert them into doubles. However, the approach you're using to convert the entire array to NSString for calculation is wrong and leads to the mentioned error.

Sample Code Causing the Error

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The Solution

To resolve this issue, you'll need to take a more native approach in Swift instead of attempting to cast the array as NSString. The use of Swift language features like compactMap serves as the right strategy for converting strings to doubles.

Step-by-Step Resolution

Convert Array of Strings to Doubles: Use compactMap to transform each string in your latitude array to its double representation.

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What does this do? The compactMap(Double.init) will iterate through the stringLatitudes array, converting valid string representations of doubles, and ignoring any nil results.

Refactor the For Loop: Instead of using an outdated Objective-C style for loop, use Swift’s half-open range operator (..<). This makes your code cleaner and avoids off-by-one errors.

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Final Note on Naming Conventions

In Swift, it’s good practice to use lowerCamelCase for variable names. Renaming custlatt to latitudeArray or similar will improve the readability of your code.

Conclusion

By following these steps, you can successfully convert an array of strings into an array of doubles and eliminate the coercion error. Adopting Swift's native practices leads to cleaner and more efficient code. Happy coding!