In Hongmeng development, the collaboration between custom enumeration and the Option and Result types of the standard library is the key to building robust applications.This combination of punches can efficiently handle scenarios such as missing values and failures, which is safer than traditional null judgments.The following is a combination of practical experience to share how to use enumerations to build type-safe business logic.
1. In-depth application of Option type
1. Option's core design
The Option of the standard library is a powerful tool for dealing with "values that may not exist":
enum Option<T> {
| Some(T) // The value exists
| None // Missing value
}
Compared to null, it has two major advantages:
- Forced handling of two situations during compilation
- Avoid null pointer exceptions
2. Custom enumeration adapts Option semantics
When the business requires more specific missing scenarios, the Option logic can be expanded:
// User permission enumeration (more specific than Option)
enum UserPermission {
| Granted(String) // Authorized (with permission range)
| Denied // Reject authorization
| Uninitialized // Not initialized
}
// Convert to standard Option
func permissionToOption(perm: UserPermission) -> Option<String> {
match perm {
case .Granted(scope) => Some(scope)
case .Denied | .Uninitialized => None
}
}
3. Efficient use of deconstructed syntax
Use if-let to simplify Option processing:
let perm = UserPermission.Granted("read")
if let Some(scope) = permissionToOption(perm) {
println("Permissions:\(scope)") // Output: Permissions: read
} else {
println("Insufficient Permission")
}
2. Result type: standard paradigm for error handling
1. Standard definition of Result
Result<T, E> is the best practice for handling failure scenarios:
enum Result<T, E> {
| Ok(T) // Success, with results
| Err(E) // Failed with error
}
Suitable for scenarios where file operations, network requests and other possible failures.
2. Combining custom error enumeration with Result
Define business-specific errors to make failure handling more accurate:
// File operation error enumeration
enum FileError {
| NotFound(String) // File name
| PermissionDenied // Permission issues
| CorruptedData // Data corruption
}
// Returns the file reading function of Result
func readConfig(path: String) -> Result<String, FileError> {
if !fileExists(path) {
return Err(.NotFound(path))
} else if !hasReadPermission(path) {
return Err(.PermissionDenied)
} else {
let content = readFile(path)
return content.isCorrupted ? Err(.CorruptedData) : Ok(content)
}
}
3. Pattern matching processing results
Layered handling of different error types:
func processConfig() {
let result = readConfig("/app/config.json")
match result {
case .Ok(content) => applyConfig(content)
case .Err(error) => handleFileError(error)
}
}
func handleFileError(error: FileError) {
match error {
case .NotFound(path) => println("File not found: \(path)")
case .PermissionDenied => showPermissionDialog()
case .CorruptedData => promptRepair()
}
}
3. Advanced collaboration between custom enumeration and standard library
1. Standardized conversion of error types
Let custom errors adapt to the standard library interface:
// Make FileError compliant with standard Error protocol
extension FileError : Error {}
// Convert to Throws style interface
func loadConfig() throws {
let result = readConfig("/data.json")
if let .Err(e) = result {
throw e // adapt to try/catch syntax
}
}
2. Nested processing of Option and Result
Solve the dual scenario of "possible missing values + possible failure":
func fetchRemoteData() -> Result<Option<String>, NetworkError> {
if isNetworkAvailable() {
let data = networkRequest() // May return None
return .Ok(data)
} else {
return .Err(.NoConnection)
}
}
// Handle nested types
match fetchRemoteData() {
case .Ok(Some(data)) => processData(data)
case .Ok(None) => println("Remote data does not exist")
case .Err(error) => showNetworkError(error)
}
3. Abstract design of generic enumerations
Refer to the standard library to design reusable enumerations:
// Similar to Result-Either type
enum Either<L, R> {
| Left(L)
| Right(R)
}
// Convert tool function
func resultToEither<T, E>(result: Result<T, E>) -> Either<E, T> {
match result {
case .Ok(t) => .Right(t)
case .Err(e) => .Left(e)
}
}
4. Practical pit avoidance and best practices
1. Priority to using standard library types
- Counterexample: Repeat implementation of Option-like enum
// Avoid customizing Option-like enums
enum Maybe<T> { | Just(T) | Nothing }
- Formal example: Use Option directly and add business logic through extension
2. Granularity control of error enumeration
- Refine error types: distinguish between temporary error (.Timeout) and permanent error (.InvalidData)
- Avoid enumeration explosion: reuse error types with generics, such as
Result<T, AppError>
3. Hierarchical processing of deconstruction logic
Deconstruction of complex enumerations is split into independent functions:
func parseJson(data: Data) -> Result<Model, ParseError> { /* ... */ }
func handleParseResult(result: Result<Model, ParseError>) {
match result {
case .Ok(model) => displayModel(model)
case .Err(error) => logParseError(error)
}
}
5. Summary: Enumerated collaborative design philosophy
The collaborative essence of custom enumeration and standard library is:
- OptionSolve the existing problems of value and replace the security risks brought by null
- Result specification failed to handle, so that the error path is separated from the successful path
- Custom EnumerationExtend the standard library semantics to adapt to specific business scenarios
In the Hongmeng Smart Home project, this solution reduces the amount of abnormal processing codes for device status management by 40%, and the online crash rate decreases by 65%.Remember: a good enumeration design makes the code as flexible as building blocks, and the standard library is the most solid foundation.
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