AI Code Explanation for Mobile App

AI-Powered Code Explanation in Mobile Applications

Code explanation is a narrower task than comprehensive Code Assist. Users paste unfamiliar code snippets or select lines, tap "Explain," and receive clear descriptions. Typical context: educational platforms, code review tools, mobile IDEs.

Programming Language Detection

Before explaining code, the language must be identified. Users rarely specify it explicitly.

On iOS, NaturalLanguage won't help—it's for human languages. Heuristics or specialized libraries are needed.

func detectLanguage(_ code: String) -> ProgrammingLanguage {
    let patterns: [(ProgrammingLanguage, [String])] = [
        (.swift, ["func ", "var ", "let ", "guard ", "@IBOutlet", "import Foundation"]),
        (.kotlin, ["fun ", "val ", "var ", "data class", "viewModelScope", "suspend fun"]),
        (.python, ["def ", "import ", "elif ", "print(", "__init__", "self."]),
        (.javascript, ["const ", "let ", "=>", "async function", "require(", "module.exports"]),
        (.typescript, [": string", ": number", "interface ", "<T>", "as unknown as"]),
        (.java, ["public class", "private void", "@Override", "System.out.println"])
    ]

    let codeShort = String(code.prefix(500))
    for (language, markers) in patterns {
        let matchCount = markers.filter { codeShort.contains($0) }.count
        if matchCount >= 2 { return language }
    }
    return .unknown
}

Marker-based heuristics work for 90% of cases. For precise detection, use the github-linguist algorithm or API (not justified for mobile clients).

Pass the detected language to the prompt—it significantly improves explanation quality, especially for languages with similar syntax (Swift vs Kotlin, JavaScript vs TypeScript).

Prompts for Different Explanation Levels

One explanation doesn't fit all users. Beginners want to know "what does this code do," while experienced developers want "why this approach instead of lazy var?"

enum ExplainLevel {
    case beginner, intermediate, expert

    var instruction: String {
        switch self {
        case .beginner:
            return "Explain this code for someone new to programming. Avoid jargon. Use simple analogies."
        case .intermediate:
            return "Explain what this code does, why key design decisions were made, and potential edge cases."
        case .expert:
            return "Analyze this code: architecture patterns used, performance implications, thread safety, potential issues."
        }
    }
}

Determine the level automatically from user behavior (how often they use beginner mode, how quickly they read responses) or provide a toggle.

Line-by-Line Explanation

For short snippets (< 20 lines), line-by-line explanation is effective:

Explain this code line by line. Format:
Line N: [explanation]
(skip blank lines and closing braces unless important)

Code:
{code}

Display as an overlay above the editor: user taps a line, an explanation popup appears nearby.

// Android Compose - line explanation on tap
@Composable
fun CodeWithExplanations(
    code: String,
    explanations: Map<Int, String>  // lineNumber -> explanation
) {
    val lines = code.lines()
    LazyColumn {
        itemsIndexed(lines) { index, line ->
            Column(modifier = Modifier.clickable { /* request explanation */ }) {
                Row {
                    Text(
                        text = "${index + 1}",
                        modifier = Modifier.width(32.dp),
                        color = MaterialTheme.colorScheme.onSurfaceVariant,
                        style = MaterialTheme.typography.bodySmall.copy(fontFamily = FontFamily.Monospace)
                    )
                    Text(
                        text = line,
                        style = MaterialTheme.typography.bodySmall.copy(fontFamily = FontFamily.Monospace)
                    )
                }
                explanations[index + 1]?.let { explanation ->
                    Text(
                        text = explanation,
                        modifier = Modifier
                            .fillMaxWidth()
                            .background(MaterialTheme.colorScheme.secondaryContainer)
                            .padding(horizontal = 8.dp, vertical = 4.dp),
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSecondaryContainer
                    )
                }
            }
        }
    }
}

Explaining Complex Constructs

Regular expressions, bitwise operations, complex generics—a separate class. Add to the prompt:

If the code contains regex patterns, explain each group separately.
If it uses bitwise operations, explain the binary logic.
If it uses generics or type constraints, explain why they're necessary.

For regex, additionally call regex101.com API or use built-in visualization through NSRegularExpression with step-by-step group explanations.

Caching Explanations

Don't explain identical code repeatedly. Cache by hash SHA256(code + language + level) with TTL of 7 days.

let cacheKey = SHA256.hash(data: Data("\(code)\(language)\(level)".utf8))
    .map { String(format: "%02x", $0) }.joined()

if let cached = explanationCache[cacheKey] {
    return cached
}

On-device: NSCache for session-local storage, Core Data / Room for persistent cache.

Timeline Estimates

Basic explanation of pasted code—2–3 days. Line-by-line mode + auto language detection + explanation levels + caching—1.5 weeks.