Bits of .NET

Creating expensive objects at startup wastes resources if they’re never used. Lazy defers creation until first access.

Without Lazy:

public class ReportService
{
    // Created on class instantiation even if never used
    private readonly PdfGenerator _pdfGen = new PdfGenerator();  // Heavy!
    private readonly ExcelExporter _excelExporter = new ExcelExporter();  // Heavy!
    
    public void GeneratePdf() => _pdfGen.Generate();
}

With Lazy:

public class ReportService
{
    // Created only when first accessed
    private readonly Lazy _pdfGen = new(() => new PdfGenerator());
    private readonly Lazy _excel = new(() => new ExcelExporter());
    
    public void GeneratePdf() => _pdfGen.Value.Generate();  // Initialized here
    public void ExportExcel() => _excel.Value.Export();     // Initialized here
}

// If only PDF is used, ExcelExporter is never created!

Thread-Safe:

// Thread-safe by default (LazyThreadSafetyMode.ExecutionAndPublication)
var lazy = new Lazy(() => new ExpensiveObject(), true);

// Multiple threads access .Value → only one creates the object

Check if Created:

if (_pdfGen.IsValueCreated)
    Console.WriteLine("PDF Generator was used");