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How to Resolve Error "CS0547: property or indexer cannot have void type" in C#

The Compiler Error CS0547 is a syntax and semantic error. The message reads: " 'PropertyName' : property or indexer cannot have void type".

In C#, a Property is designed to represent data—it allows you to read ("get") or write ("set") a value. Because a property conceptually represents a value (like a variable), it must have a valid data type (like int, string, or a custom class) that defines what kind of data passes through it. void means "no data," which creates a logical contradiction: you cannot "get" nothing, nor can you assign a value to "nothing".

This guide explains why properties require types and how to refactor your code if you intended to perform an action instead.

Understanding Property Semantics​

  • Variables/Fields: Store data. Must have a type.
  • Properties: Encapsulate fields. Must have the same type as the data they represent.
  • Methods: Perform actions. Can return void (no result).

If you declare public void MyProp { get; set; }, the compiler asks: "When someone writes var x = obj.MyProp, what is stored in x?" Since void cannot be stored, the definition is invalid.

Scenario 1: Defining a Void Property​

This error usually happens when a developer creates a "Write-Only" property intending to trigger an action (like logging or resetting state) without returning any value, so they instinctively type void.

Example of error:

public class Logger
{
    // ⛔️ Error CS0547: 'Logger.LogEntry' : property or indexer cannot have void type.
    // Properties must represent a value, even if they are write-only.
    public void LogEntry
    {
        set { System.Console.WriteLine(value); }
    }
}

Solution 1: Assign a Specific Data Type​

If the property is meant to accept data (via the set accessor), you must declare the property with the type of data it accepts.

Solution: change void to the type of the value keyword used in the setter.

public class Logger
{
    // ✅ Correct: The property accepts a 'string'.
    // Even without a getter, the type defines what can be assigned to it.
    public string LogEntry
    {
        set { System.Console.WriteLine(value); }
    }
}

// Usage:
// logger.LogEntry = "Message";

Solution 2: Convert to a Method (Action)​

In C# design guidelines, properties should generally represent state, not actions. If your property logic performs a complex operation, has side effects, or "does something" rather than "setting a value," it should be a Method. Methods naturally support void.

Solution: refactor the property into a method.

public class Logger
{
    // ✅ Correct: Methods are designed for actions and can return void.
    public void LogEntry(string message)
    {
        System.Console.WriteLine(message);
    }
}

// Usage:
// logger.LogEntry("Message");

Conclusion​

CS0547 enforces the distinction between data and behavior.

  1. Check the Intent: Does this member represent a piece of data (Name, ID, Color)?
    • Yes: Give it a Type (string, int, Color).
  2. Does it perform an action? (Reset, Log, Calculate)?
    • Yes: Change it from a Property to a Method (void DoWork()).

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