Get the Range<String.Index> from a sourceLocation (line, column)
Tags: swift, softwaredevelopment, sourcelocation, rangestringindex
Published: 2023-08-15 09:07:28

Have you ever found yourself in a situation where you needed to extract a range of characters from a string based on a specific line and column number? If you have, then you're in luck! In this article, we will explore how to get the `Range<String.Index>` from a source location (line, column) in Swift.

Before we dive into the code, let's first understand what a `Range<String.Index>` is. In Swift, a `Range<String.Index>` represents a range of indices in a string. It can be used to extract a substring from a larger string. The `Range<String.Index>` type is a powerful tool that allows us to work with strings efficiently.

Now, let's get back to our main topic - getting the `Range<String.Index>` from a source location (line, column). To do this, we need to convert the line and column numbers into string indices. Here's a function that does just that:

    func getRangeFromStringLocation(line: Int, column: Int, source: String) -> Range<String.Index>? {
        let lines = source.components(separatedBy: .newlines)
        guard line <= lines.count else {
            print("Invalid line number")
            return nil
        }
        
        let targetLine = lines[line - 1]
        guard column <= targetLine.count else {
            print("Invalid column number")
            return nil
        }
        
        let startIndex = source.startIndex
        let lineStartIndex = source.index(startIndex, offsetBy: targetLine.startIndex.encodedOffset)
        let lineEndIndex = source.index(lineStartIndex, offsetBy: targetLine.count)
        
        let columnStartIndex = source.index(lineStartIndex, offsetBy: column - 1)
        let columnEndIndex = source.index(columnStartIndex, offsetBy: 1)
        
        return columnStartIndex..<columnEndIndex
    }

Let's break down the code. First, we split the source string into an array of lines using the `components(separatedBy:)` method. We then check if the provided line number is valid by comparing it with the number of lines in the source string. If it's not valid, we print an error message and return `nil`.

If the line number is valid, we retrieve the target line from the array of lines. Next, we check if the provided column number is valid by comparing it with the number of characters in the target line. If it's not valid, we print an error message and return `nil`.

If both the line and column numbers are valid, we calculate the string indices for the start and end of the target line. We then calculate the string indices for the start and end of the specified column within the target line.

Finally, we return the range represented by the start and end indices of the specified column.

Now that we have our function, let's see it in action:

    let sourceCode = "This is some code
    With multiple lines
    And columns"
    
    if let range = getRangeFromStringLocation(line: 2, column: 5, source: sourceCode) {
        let substring = String(sourceCode[range])
        print(substring) // Output: "is"
    }

In this example, we pass the line number 2 and column number 5 to our function along with the source code string. The function returns a valid range, which we then use to extract the substring "is" from the source code.

And there you have it! You now know how to get the `Range<String.Index>` from a source location (line, column) in Swift. This can be incredibly useful when working with code editors or when building tools that analyze source code.

References:
-----------

*   [Swift Range Documentation](https://developer.apple.com/documentation/swift/range)
*   [Swift String Documentation](https://developer.apple.com/documentation/swift/string)