PHP 8.3 Read-Only Property Guide

Chapter 1: Overview of PHP 8.3 Read-only Property Default Value Settings

In PHP 8.3, the functionality of read-only properties was further enhanced, allowing developers to set default values ​​when declaring read-only properties. This improvement increases the flexibility of class design, enabling the definition of read-only properties with an initial state without relying on constructor initialization.

Syntax support for read-only properties and default values

Starting with PHP 8.3, you can specify scalar or static default values ​​directly in a class for read-only properties without having to assign them through the constructor. This simplifies code structure and enhances readability.

// Example: Read-only property with default value 
class Configuration 
{ 
    public readonly string $host = 'localhost'; // Valid: default value 
    public readonly int $port = 8080; 
 
    public function display(): void 
    { 
        echo "Host: {$this->host}, Port: {$this->port}"; 
    } 
} 
 
$config = new Configuration(); 
$config->display(); // Output: Host: localhost, Port: 8080

In the code above, $host `x` and `  $port y` are declared as read-only properties and assigned default values. They can be accessed directly after instantiation and cannot be reassigned.

Supported default value types

PHP 8.3 allows the following types of default values ​​for read-only properties:

• Scalar values ​​(such as strings, integers, booleans, and floating-point numbers)
• null value
• Array literals (note the syntax restrictions)

However, expressions or function calls are not allowed as default values; for example,   dynamic calculations such as time() `or`  are still restricted.self::CONSTANT + 1

Comparison with constructor initialization

Initialization method	Does it support default values?	Applicable Scenarios
Direct assignment (PHP 8.3)	yes	Fixed configuration, constant behavior
Constructor assignment	No (manual parameter passing is required)	Dynamic injection, runtime determination

Chapter 2: Underlying Mechanism Analysis of Read-Only Attributes and Default Values

2.1 Syntax definition and restrictions of read-only attributes

In object-oriented programming, once a read-only property is defined using specific syntax, its value can only be assigned during the initialization phase and cannot be changed subsequently. For example, in C#:

public class User 
{ 
    public string Id { get; } 
    
    public User(string id) 
    { 
        Id = id; // Can be assigned a value in the constructor 
    } 
}

In the code above, Id the properties only contain  get accessors and are initialized in the constructor. Any subsequent attempts to modify  Id them will result in a compilation error.

Core constraints

• Assignment can only be done at the time of declaration or within the constructor.
• Modification is not allowed in ordinary methods or property setters.
• Complex initialization logic other than automatic attributes is not supported.

This mechanism ensures the immutability of object state, providing language-level guarantees for thread safety and data consistency.

2.2 Analysis of the range of data types supported by default values

In modern programming languages, different data types show significant differences in their support for default values. Understanding these differences helps improve code robustness and maintainability.

Basic data types

Basic data types such as integers, floating-point numbers, and booleans typically have explicit default values. For example, in Go, uninitialized variables are automatically assigned the value zero.

var a int      // Default Value is 0
var b float64  // Default Value is 0.0
var c bool     // Default Value is false
var d string   // Default Value is ""

The code above demonstrates Go’s zero-value mechanism for primitive types. This mechanism ensures that variables are safe to use immediately after declaration, avoiding undefined behavior.

Composite data type support

• Arrays: Elements are assigned a zero value according to their type.
• Structure: Each field is initialized to its default value.
• Pointers: default to nil

type	default value
int	0
string	“”
pointer	nil

2.3 Attribute Initialization Timing and Constructor Coordination Logic

In object-oriented programming, the timing of property initialization directly affects the consistency of an object’s state. Typically, properties are declared during class definition, but their actual assignment is often delayed until the constructor execution phase.

Initialization order resolution

Property initialization is performed according to the following priority:

1. Assigning default values ​​directly to a class
2. Reassignment or computation assignment within the constructor
3. Dependency injection frameworks inject values ​​(such as Spring).

Code Examples and Analysis

public class User {
    private String name = "default"; // Stage 1: Initialization during Declaration
    private int age;
 
    public User(String name, int age) {
        this.name = name; // Stage 2: constructor override
        this.age = age;
    }
}

In the code above, name a default value is first assigned, and then overridden by the parameter passed in during the constructor. This demonstrates the phased nature of initialization: declarative initialization provides a safe default state for subsequent constructions, while the constructor completes the customized configuration.

Synergistic Logic Significance

This mechanism ensures the integrity and flexibility of data during object creation, and avoids the exposure of uninitialized states.

2.4 Discussion of the Boundary Between Compile-Time Constants and Runtime Expressions

In modern programming languages, the distinction between compile-time constants and runtime expressions directly impacts program performance and security. Compile-time constants have their values ​​determined during code generation, while runtime expressions are evaluated during program execution.

Constant folding and optimization

The compiler can perform folding optimization on pure constant expressions:

const factor = 2
const result = 10 * factor + 5 // The compilation period is calculated as 25

The expression consists entirely of constants, which the compiler directly replaces with the literal 25, reducing runtime overhead.

Limitations of runtime expressions

Expressions involving function calls or external input cannot be evaluated at compile time:

var input int
fmt.Scanf("%d", &input)
const dynamic = input * 2 // Error: Cannot assign runtime value to const

In this example,  input the data comes from user input and is runtime data, so it cannot be included in constant definition.

type	When to evaluate	Typical example
compile-time constants	Compilation time	10 + 5, “hello” + “world”
Runtime expressions	During execution	time.Now(), rand.Int()

2.5 Implementation Principle of Read-Only Attributes from the Bytecode Level

At the bytecode level, the implementation of read-only properties relies on field access flags and property encapsulation mechanisms. The JVM restricts field modification and external access through ACC_FINALflags ACC_PRIVATE.

Access flags in bytecode

Taking a Java class as an example, fields declared as `id` will contain `id` and `id` flags public final String NAME = "Java";in the bytecode generated after compilation :ACC_PUBLICACC_FINAL

field NAME:Ljava/lang/String; 
  flags public final 
  constant "Java"

putfieldWhen an instruction attempts to modify this field putstatic, the JVM checks whether it is marked as such final; if it has been initialized, it throws an exception.

Read-only guarantee mechanism

• The compiler prevents finalfields from being assigned duplicate values.
• The JVM verifies field initialization logic during the class loading phase.
• Runtime access control prevents reflection-based tampering (depending on the security manager).

Chapter 3: Common Use Cases and Coding Practices

3.1 Encapsulation of default values ​​for read-only properties in configuration classes

In configuration management, encapsulating read-only properties with default values ​​helps improve code maintainability and security. Presetting immutable properties through constructors or static factory methods can prevent accidental runtime modifications.

Default value declaration method

When initializing a struct, combine private fields with public read-only accessors to ensure that values ​​cannot be changed once set:

type Config struct {
    host string
    port int
}
 
func NewConfig() *Config {
    return &Config{
        host: "localhost",
        port: 8080,
    }
}

In the code above, the fields are not exported host and  port cannot be directly modified externally; they can only be accessed through methods.

Advantages Analysis

• Enhance data consistency: Default values ​​are defined centrally to avoid discrepancies caused by scattered assignment.
• Supports secure sharing: Read-only semantics allow multiple coroutines to securely read configuration instances.

3.2 Initialization strategy for security fields in DTO objects

When constructing a Data Transfer Object (DTO), sensitive fields such as passwords and tokens must be securely initialized to prevent accidental information leakage.

Default value clearing strategy

All security-related fields should be explicitly initialized to safe default values ​​during instantiation, avoiding the use of language default null references or zero-value speculation.

public class UserDto { 
    private String username; 
    private String password = ""; // Explicitly initialized to an empty string 
    private String token = ""; 
 
    // Forced reset in the constructor 
    public UserDto() { 
        this.password = ""; 
        this.token = ""; 
    } 
}

The code above ensures that even if an instance is created using reflection, sensitive fields will not expose historical data.

Best practices for field initialization

• Setting sensitive fields to null is prohibited to circumvent serialization checks.
• Use the constructor or builder pattern to set up initialization logic.
• Combine with annotations such as @JsonIgnore to prevent serialization output.

3.3 Simplify dependency injection container configuration using default values

In the configuration of a dependency injection (DI) container, frequently declaring underlying services or predictable dependencies increases configuration complexity. Explicit configuration items can be significantly reduced by injecting default values ​​for parameters or constructors.

Use cases for default parameters

When a dependency uses the same implementation in most cases, a default value can be specified in the class constructor to avoid repeated declarations every time it is registered.

class OrderProcessor {
    public function __construct(
        private PaymentGatewayInterface $gateway = null,
        private LoggerInterface $logger = new NullLogger()
    ) {
        if ($this->gateway === null) {
            $this->gateway = new DefaultPaymentGateway();
        }
    }
}

In the code above, if no payment gateway or logger is passed in, the container will automatically use the default implementation, reducing the configuration burden.

Configuration optimization comparison

Way	Configuration quantity	Maintainability
Fully explicit injection	high	Low
Default value auxiliary injection	Low	high

Chapter 4: Advanced Techniques and Avoiding Potential Traps

4.1 The correct way to declare default values ​​for array types

In Go, an array is a fixed-length sequence of elements of the same type. When an array is declared but not explicitly initialized, its elements are automatically assigned zero values ​​of their respective types.

Default values ​​for arrays of primitive types

For example, to declare an integer array:

var nums [3]int
fmt.Println(nums) // output: [0 0 0]

The array has a length of 3, and each element defaults to intthe zero value 0 of its type.

Default value rules for composite types

For arrays of structures, their fields also follow the zero-value principle:

type User struct {
    Name string
    Age  int
}
var users [2]User
fmt.Println(users) // [{ 0} { 0}]

NameThe field is an empty string, Agewhich is 0, conforming to the default value of its respective type.

• Numeric type: 0
• String type: “”
• Boolean type: false
• Pointer or interface: nil

4.2 Analysis of Attribute Inheritance Issues When Collaborating with Traits

In object-oriented design, while the trait mechanism enhances code reusability, it can easily lead to conflicts in property inheritance. When multiple traits define properties with the same name, the language usually cannot automatically merge them, resulting in overwriting or errors.

Typical conflict scenarios

trait Timestamp { 
    protected $createdAt = null; 
} 
 
trait SoftDelete { 
    protected $createdAt = null; // Conflict: same name property 
} 
class User { 
    use Timestamp, SoftDelete; // PHP will throw a fatal error 
}

In the code above, both traits are declared $createdAt, and PHP cannot determine their priority, resulting in compilation failure.

Solution Comparison

Strategy	Implementation	limitation
Explicit rewriting	Redefining properties in a class	Breaking trait encapsulation
Alias ​​mechanism	use T1, T2::prop as prop2	Only applicable to methods, not properties.

Currently, mainstream languages ​​do not provide attribute-level conflict resolution syntax, requiring developers to manually coordinate namespaces.

4.3 The impact of reflection operations on the default values ​​of read-only properties

In Go, reflection allows programs to dynamically access and modify the values ​​of variables at runtime. However, the behavior of reflection is limited when the target property is a read-only field in a struct (such as an unexported field or a default value set by the constructor).

Reflection modifies the boundary conditions of a read-only field

Attempting to modify non-addressable or non-exported fields via reflection will result in a runtime panic. Only exportable fields with accessible addresses can be safely modified.

type Config struct {
    ReadOnly string
    mutable  int
}
 
c := Config{ReadOnly: "initial"}
v := reflect.ValueOf(&c).Elem()
f := v.FieldByName("ReadOnly")
if f.CanSet() {
    f.SetString("modified")
}

In the code above, ReadOnly the exported field CanSet() returns true and can be successfully modified; however,  mutable because the first letter is lowercase, it cannot be set via reflection.

Risk of default value overriding

When using reflection to batch initialize configurations, default values ​​that should remain unchanged by design may be accidentally overwritten. It is recommended to verify the settableness and original value state of fields before performing the operation to avoid breaking the encapsulation logic.

4.4 Compatibility Handling: Considerations for Migrating from Older Versions to 8.3

When upgrading to version 8.3, pay close attention to API changes and deprecated features. Some older interfaces have been removed; it is recommended to use the new asynchronous call model instead.

Example of replacing obsolete interfaces

// Old version (deprecated)
client.Query("select * from users")
 
// Recommend for new version
client.ExecuteContext(ctx, "SELECT * FROM users WHERE status = $1", "active")

The code above ExecuteContext introduces context control and parameterized queries to improve security and traceability.

Compatibility Checklist

• Verify if third-party plugins support 8.3+
• Check for changes in the configuration file structure, such as  config.yaml those in [file name]  storage.engine that have been migrated to [location]. engine.storage
• Update the client SDK to v2.5 or higher to support the new authentication mechanism.

Data migration impact

Components	Change type	Handling suggestions
User Session Module	Structural changes	Execute migrate-session –version=8.3
Log format	Field renaming	Update ELK parsing rules

Chapter 5: Future Outlook and Best Practice Summary

The continuous evolution of cloud-native architecture

Modern application deployments are rapidly converging on Kubernetes and service meshes. When enterprises implement traffic governance using Istio, they often use the following configurations for canary releases:

apiVersion: networking.istio.io/v1beta1
kind: VirtualService
metadata:
  name: user-service-route
spec:
  hosts:
    - user-service
  http:
  - route:
    - destination:
        host: user-service
        subset: v1
      weight: 90
    - destination:
        host: user-service
        subset: v2
      weight: 10

This strategy can effectively reduce the risk of launching a new version. One fintech company used this strategy to reduce its online failure rate by 67%.

Automated Safe Left Shift Practice

DevSecOps requires embedding security checks into the CI/CD process. The following toolchain combination is recommended:

• Trivy scans for container image vulnerabilities
• Checkmarx Static Code Analysis
• Open Policy Agent verifies resource configuration compliance.

After integrating the aforementioned tools into GitLab Pipeline, an e-commerce platform reduced its average vulnerability repair time from 48 hours to 3 hours.

Construction of observable systems

A complete monitoring loop needs to cover metrics, logs, and tracing. The following technology stack combination is recommended:

type	tool	use
Metrics	Prometheus + Grafana	System performance monitoring
Logs	Loki + Promtail	Lightweight log aggregation
Tracing	Jaeger	Distributed call tracing

A logistics platform has reduced the root cause location time for cross-microservice delays by 80% through this system.