Caller Information Attributes

Caller information attributes let the compiler automatically pass details about the calling code into a method. They are especially useful for logging, diagnostics, argument validation helpers, and lightweight tracing.

Original Microsoft Learn reference: Caller information.

This feature matters because it removes a lot of repetitive manual strings while keeping diagnostic code more accurate and easier to maintain.

The core idea

When a method parameter is decorated with a caller information attribute, the compiler can fill in that parameter at the call site.

The three most common attributes are:

• CallerMemberName
• CallerFilePath
• CallerLineNumber

flowchart TD
    A["Method call"] --> B["Compiler injects caller info"]
    B --> C["Member name"]
    B --> D["File path"]
    B --> E["Line number"]

A simple example

using System.Runtime.CompilerServices;

static void Log(string message,
    [CallerMemberName] string memberName = "",
    [CallerLineNumber] int lineNumber = 0)
{
    Console.WriteLine($"[{memberName}:{lineNumber}] {message}");
}

Log("Starting work");

The caller does not supply memberName or lineNumber, but the method still receives them.

Why this is useful

Without caller information attributes, logging helpers often require extra strings that callers must remember to keep in sync.

Log("Save started", "SaveCustomer");

That is fragile. If the method is renamed, the string may become wrong. Caller information attributes avoid that duplication because the compiler derives the information directly from the call site.

CallerMemberName

CallerMemberName provides the name of the calling member.

using System.Runtime.CompilerServices;

static void Notify([CallerMemberName] string memberName = "")
{
    Console.WriteLine($"Called from: {memberName}");
}

static void ProcessOrder()
{
    Notify();
}

This prints ProcessOrder.

One common use is property-change notification in UI or state-management code.

CallerLineNumber

CallerLineNumber captures the source line where the call appears.

using System.Runtime.CompilerServices;

static void TraceStep(
    string message,
    [CallerLineNumber] int lineNumber = 0)
{
    Console.WriteLine($"Line {lineNumber}: {message}");
}

This is most useful in diagnostics, especially when you want lightweight tracing without a full debugger attached.

CallerFilePath

CallerFilePath captures the full source file path of the call site.

using System.Runtime.CompilerServices;

static void TraceFile([CallerFilePath] string filePath = "")
{
    Console.WriteLine(filePath);
}

This can help in debugging tools or test helpers, but be careful about logging full file paths in production because they may expose environment-specific details.

Argument validation helpers

Caller information attributes also connect nicely with reusable validation helpers.

using System.Runtime.CompilerServices;

static void EnsureNotNull<T>(
    T value,
    [CallerArgumentExpression(nameof(value))] string expression = "")
    where T : class
{
    ArgumentNullException.ThrowIfNull(value, expression);
}

If you call EnsureNotNull(customer.Name);, the helper can report the original expression text automatically.

CallerArgumentExpression is newer than the original caller info attributes, but it belongs to the same family of compile-time call-site assistance.

A practical example

using System.Runtime.CompilerServices;

public sealed class OperationTracker
{
    public void Mark(
        string status,
        [CallerMemberName] string memberName = "",
        [CallerLineNumber] int lineNumber = 0)
    {
        Console.WriteLine($"{memberName} at line {lineNumber}: {status}");
    }
}

OperationTracker tracker = new();
tracker.Mark("Loaded configuration");

This kind of helper is useful in small tools, sample code, and local diagnostics.

What the compiler is really doing

It helps to think of the compiler as rewriting the call with extra arguments.

Conceptually, this:

tracker.Mark("Loaded configuration");

becomes something like this:

tracker.Mark("Loaded configuration", "Main", 27);

You usually do not write that expanded form yourself, but it explains why the feature has almost no runtime mystery.

Common mistakes

• Forgetting that these attributes work through optional parameters.
• Logging full file paths in environments where that data should stay private.
• Using caller info as a replacement for structured logging design.
• Assuming the values are discovered at runtime through reflection. They are usually inserted by the compiler.

Practical guidance

• Use caller information attributes to reduce repetitive diagnostic boilerplate.
• Prefer them for helper methods, tracing utilities, and validation infrastructure.
• Treat CallerFilePath carefully in production logs.
• Keep the surrounding logging design clear; caller info improves context, but it does not replace thoughtful diagnostics.

Summary

• caller information attributes let the compiler supply call-site details automatically
• CallerMemberName, CallerLineNumber, and CallerFilePath are the main classic attributes
• CallerArgumentExpression extends the same idea to validation and diagnostics
• these features reduce fragile manual strings and improve helper APIs
• they are most valuable in tracing, validation, and diagnostic utilities

Practice

Write a small logging helper that prints the caller member name automatically.

As a second exercise, create an EnsureNotNull helper that uses CallerArgumentExpression so the thrown exception reports the original argument expression.