Скачать или смотреть How to Calculate the Correct Date from a String in Swift 5

Learn how to extract and calculate time values from strings in `Swift 5` using regex and DateFormatter.
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How to Calculate the Correct Date from a String in Swift 5

In today's digital world, working with time is a common requirement in application development. For developers using Swift 5, a frequent challenge is parsing and manipulating time strings effectively. If you've ever received response data that includes work hours in the format of a string, calculating start and end times can seem daunting. In this guide, we will tackle this problem head-on and guide you through the process of extracting time values from a string using regular expressions, and calculating the difference between them.

The Problem: Parsing Work Hours from a String

Imagine you have received a string from your backend that defines work hours:

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Your task is to extract the start time (9:00) and end time (18:00), and to determine the time difference between the two. If you're not familiar with regular expressions or date manipulation in Swift, this might feel like a challenge. But fear not! We will break it down step by step.

Step 1: Setting Up the Regex Pattern

Regular expressions (regex) can be incredibly powerful for parsing strings. For our scenario, we need a regex pattern that captures the start and end times from the provided work hours format. Here’s the regex pattern we will use:

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Explanation of the Regex Pattern

^ asserts position at the start of a line.

[A-Z]-[A-Z] matches a single uppercase character, a dash, and another uppercase character (e.g., M-F).

\s{1} matches exactly one whitespace character.

\d{1,2} matches one or two digits, which represent the hour part of the time.

: matches the colon character.

\d{2} matches exactly two digits, representing the minute part.

\s{1}-\s{1} matches the dash and spaces surrounding it.

$ asserts position at the end of a line.

Step 2: Implementing the Regex in Swift

Using the regex in Swift will allow us to extract the needed times. Below is the code to achieve that:

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Expected Output

When this code runs, you should see the following printed to your console:

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Step 3: Calculating the Time Difference

Now that you have both the start and end times, the next step is to calculate the time difference in hours. To do this, we first need to convert our time strings into a measurable format.

Adding a Computed Property for Time Conversion

We’ll extend StringProtocol with a computed property to convert a time string into minutes:

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Calculating Minutes and Hours

With the above extension, we can now easily calculate the minutes between the start and end times:

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This will give you the difference in hours between the two time strings.

Conclusion

Parsing time strings and calculating differences may seem complex at first, but with the power of regex and Swift’s string manipulation capabilities, it can become a straightforward process. Using the steps outlined in this post, you can efficiently extract start and end times from a provided string and calculate the time difference.

So the next time you encounter a string with work hours, you'll be well-equipped to handle it with ease!