SafeExpression

SafeExpression is a small Swift package that safely wraps NSExpression(format:), protecting your app from crashes caused by malformed expressions. If parsing fails, the wrapper throws a Swift Error instead of crashing.

🔐 Why?

Apple's NSExpression(format:) can crash your app if you pass an invalid format string. SafeExpression prevents that by catching Objective-C exceptions and converting them into Swift throws.

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✅ Features

• Safe parsing of format strings
• Throws descriptive errors instead of crashing
• Usable in 100% Swift projects (no need for bridging headers)

🔧 Installation

Swift Package Manager

Add the following to your Package.swift:

.package(url: "https://github.com/dimkah/SafeExpression.git", from: "1.0.0")

Xcode

1. Open your project in Xcode.
2. Go to File > Swift Packages > Add Package Dependency.
3. Enter the URL: https://github.com/dimkah/SafeExpression.git.
4. Choose the version you want to use (e.g., 1.0.0).

✅ Usage

Import the module

import SafeExpression

Create a SafeExpression

do {
    let expression = try SafeExpressionWrapper.expression(format: "(5 + 2 * 3") // Invalid format (missing closing parenthesis)
    let result = expression.expressionValue(with: nil, context: nil)
    print("Result:", result ?? "nil") // Will not be reached since the expression is invalid
} catch {
    print("Expression error:", error.localizedDescription) // Handle the error
    // Output: Expression error: Invalid expression format
    // or similar error message
    // depending on the specific issue with the format string.
}

💡 Why use SafeExpression?

Without SafeExpression:

let expression = NSExpression(format: "5 + (2 *") // 💥 Crash!

With SafeExpression:

do {
    let expression = try SafeExpressionWrapper.expression(format: "5 + (2 *")
} catch {
    print("Invalid expression:", error.localizedDescription)
}

✅ No crash — just a regular Swift error.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Contributing

Contributions are welcome! Please feel free to submit a pull request or open an issue if you find a bug or have a feature request.