HarmonyOS Next enumeration type performance optimization: memory and matching efficiency

In HarmonyOS Next development, the performance of enum types (enum) is crucial to resource-constrained devices (such as IoT terminals, embedded devices).The enumeration of Cangjie language achieves a balance between memory usage and matching efficiency through constructor design, matching order optimization and compiler characteristics.This article combines document knowledge points to analyze the performance optimization strategies of enumeration types.

1. Enumerated memory layout and constructor design

1. Memory usage of no parameters enumeration

The parameterless enumeration takes up 1 byte in memory and is used to store the constructor index.For example:

enum SimpleState { | Idle | Running | Stopped } // Takes up 1 byte

• The compiler assigns a unique index to each constructor (such as Idle=0, Running=1, Stopped=2) to quickly access the state through the index.

2. Memory extension with parameter enumeration

The memory usage of parameter enumeration depends on the parameter type, following the "maximum constructor principle":

enum ComplexData {
| IntValue(Int64) // Takes up 8 bytes (Int64)
| DoubleValue(Double) // Takes up 8 bytes (Double)
| StringValue(String) // Occupy pointer size (usually 8 bytes)
}

• The memory footprint of all constructors must be aligned to the maximum parameter type, and in this case it is 8 bytes.

3. Practice of reducing enum volume

• Avoid redundant parameters: If some constructor parameters can be omitted, split into non-parameter + parameter constructor:

  enum ControlCommand {
| PowerOn | PowerOff // Parameterless constructor (1 byte each)
| SetBrightness(UInt8) // Parameter constructor (1 byte + UInt8=2 bytes)
  }

• Use smaller data types: Use UInt8 instead of UInt32 to store status codes to reduce memory usage.

2. Optimization of efficiency of pattern matching

1. Effect of matching order on performance

The match expression matches the case branch in order, placing the high-frequency state on top reduces the number of matches:

enum NetworkEvent {
    | PacketReceived(UInt32)
    | ConnectionLost
    | Heartbeat
}

func handleEvent(event: NetworkEvent) {
    match (event) {
case .PacketReceived(_): // High-frequency event priority matching
            processPacket()
case .Heartbeat: // Sub-high frequency
            updateHeartbeatTime()
case .ConnectionLost: // Low frequency event
            reconnect()
    }
}

2. Avoid redundant matching logic

Use | to combine similar patterns to reduce the number of branches:

enum InputKey {
    | KeyA | KeyB | KeyC | KeyD | KeyE
    | FunctionKey(Int)
}

func handleKey(key: InputKey) {
    match (key) {
case .KeyA | .KeyB | .KeyC => // Combination matching letter keys
            handleLetterKey()
        case .KeyD | .KeyE =>
            handleSpecialLetterKey()
        case .FunctionKey(n) where n < 10 =>
            handleFunctionKey(n)
        default:
            ignoreKey()
    }
}

3. Compiler optimization strategy

The Cangjie compiler will optimize the enum matching as follows:

• Jump table optimization: For the non-argument enumeration, generate a jump table to achieve O(1) time complexity matching;
• ** Conditional branch optimization**: Use efficient conditional judgment chains for branches with parameter enumeration or where conditions.

3. Performance considerations for recursive enumeration

1. Memory and stack overhead of recursive enumeration

Recursive enumerations (such as expression trees) will cause the stack space occupation to increase with the recursive depth. Pay attention to the risk of stack overflow:

enum Expr {
    | Num(Int)
    | Add(Expr, Expr)
    | Sub(Expr, Expr)
}

func evaluate(expr: Expr) -> Int {
    match (expr) {
        case .Num(n) => n
case .Add(l, r) => evaluate(l) + evaluate(r) // The depth of the recursion depends on the number of nested layers of the expression
        case .Sub(l, r) => evaluate(l) - evaluate(r)
    }
}

• Optimization Solution: For recursive enumerations with greater depth, use iterative or tail recursive optimization instead (if the compiler supports it).

2. Tail recursive optimization example

func factorial(n: Int, acc: Int = 1) -> Int {
    enum FactState { | Init(Int, Int) | Step(Int, Int) }
    var state: FactState = .Init(n, acc)

    while true {
        match (state) {
            case .Init(0, acc) => return acc
            case .Init(n, acc) => state = .Step(n-1, n*acc)
            case .Step(0, acc) => return acc
            case .Step(n, acc) => state = .Step(n-1, n*acc)
        }
    }
}

4. Practical scenarios: Enumeration optimization of low-power devices

1. Sensor status enumeration design

In smart home sensors, use parameterless enumeration to represent states to reduce memory usage:

enum SensorStatus {
    | Normal  // 0
    | LowBattery  // 1
    | Fault  // 2
}

// Only 100 bytes are required to store 100 sensor status
var statuses: Array<SensorStatus> = Array(repeating: .Normal, count: 100)

2. Quick matching interrupt processing

In embedded system interrupt processing, place the high frequency interrupt type on the top of the matching branch:

enum Interrupt {
    | TimerOverflow
    | ADCComplete
    | UARTDataReady
    | GPIOEdge
}

func handleInterrupt(irq: Interrupt) {
    match (irq) {
case .UARTDataReady: // High-frequency communication interrupts are processed first
            readUARTBuffer()
case .TimerOverflow: // Sub-high frequency timing interrupt
            updateTimer()
case .ADCComplete: // Analog-to-digital conversion is completed
            processADCData()
case .GPIOEdge: // Low frequency IO interrupt
            handleGPIOEvent()
    }
}

5. Performance comparison and best practices

1. Memory usage comparison

Enumeration type	Number of constructors	Memory usage/instance	Typical scenarios
No parameter enumeration	3	1 byte	State machine, mode identification
Parameter Enumeration (Int)	2	8 bytes	Status with numerical parameters
Recursive enumeration (expression tree)	3	Dynamic (recursive depth)	parser, compiler front-end

2. Matching efficiency best practices

• Priority specific mode: Put the specific state (such as .Error) before the general mode (such as _);
• Avoid over-necking: Pattern matching that exceeds 3 layers of nesting should be disassembled into independent functions;
• Use syntax sugar: For single constructor enumeration, use the constructor name directly as the variable name (such as let .Init = state).

Summarize

The performance optimization of HarmonyOS Next enumeration type needs to start from the two aspects of ** memory layout** and ** matching logic**:

1. Memory optimization: Reduce instance volume through parameterless constructors and small data types to avoid redundant parameters;
2. Efficiency optimization: Reasonably design the matching order, use compiler optimization features to avoid the stack risks of recursive enumeration.