Example.SmartContract.Modifier

Neo N3 Modifier Smart Contract Example

Overview

This example demonstrates how to implement and use custom modifiers in Neo N3 smart contracts. Modifiers provide a powerful way to enhance method functionality with pre-conditions and post-conditions, improving code reusability, readability, and security by centralizing common validation logic.

Key Features

• Custom modifier attribute creation
• Access control implementation
• Method decoration with modifiers
• Pre-condition and post-condition handling
• Reusable authorization logic

Technical Implementation

The SampleModifier contract demonstrates two key aspects of Neo N3 modifiers:

Modifier Definition

The example shows how to:

• Create a custom OnlyOwnerAttribute that inherits from ModifierAttribute
• Define constructor parameters for configurable modifiers
• Implement Enter() method for pre-execution validation
• Implement Exit() method for post-execution operations

Modifier Usage

The contract demonstrates:

• Applying the custom modifier to a contract method
• Passing configuration parameters to the modifier
• Automatic validation before method execution

How Neo N3 Modifiers Work

Modifiers in Neo N3 follow this execution flow:

1. When a method with a modifier is called, the modifier's Enter() method is executed first
2. If the Enter() method completes without exceptions, the decorated method executes
3. After the method execution (even if it fails), the modifier's Exit() method is called
4. If the Enter() method throws an exception, the decorated method is not executed

Common Modifier Patterns

The example demonstrates the most common modifier pattern:

• Access Control: Restricting method access to specific addresses
• Ownership Validation: Ensuring the caller has appropriate permissions

Other common patterns that can be implemented with modifiers:

• Reentrancy Guards: Preventing recursive calls
• State Validation: Ensuring contract is in a valid state for the operation
• Pause Mechanism: Enabling/disabling contract functionality

Security Benefits

Modifiers improve contract security by:

• Centralizing validation logic to avoid repetition
• Enforcing consistent access control
• Preventing execution when conditions aren't met
• Making authorization requirements explicit

Customization Guide

To adapt this example for your own modifiers:

1. Create a new class that inherits from ModifierAttribute
2. Implement the Enter() and Exit() methods with your logic
3. Add any configuration parameters to the constructor
4. Apply your new modifier to methods using the attribute syntax

Educational Value

This example teaches:

• How to create and use custom modifiers
• Implementing access control patterns
• C# attribute-based programming
• Pre-condition and post-condition handling
• Code organization for reusable validation logic

Modifiers are a powerful tool for Neo N3 smart contract development, enabling more maintainable, secure, and expressive code by separating cross-cutting concerns from business logic.