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373 posts · Page 2 of 38

2026-10-29 comparison csharp dotnet

Try pattern vs throwing exceptions for expected failures in C#

Return bool from a TryX method when failure is an ordinary outcome the caller will branch on, and throw when it is a bug or a broken precondition. Measured on .NET 10.0.10: a failed int.TryParse costs 4.9 ns, a caught FormatException costs 2,487 ns.

2026-10-28 errors csharp dotnet

Fix: Cannot access a disposed object. Object name: 'IServiceProvider'

Code resolved a service from a DI scope or root provider after it was disposed. Capture IServiceScopeFactory instead of IServiceProvider and create a fresh scope where the work runs.

2026-10-28 errors csharp csharp-14

Fix: [MemberNotNull] has no effect on a static factory method and CS8618 still fires

CS8618 is checked when the constructor exits, and [MemberNotNull] on a static method is silently ignored for instance members. Pass the values into a private constructor instead.

2026-10-27 errors ef-core dotnet

Fix: The property 'X' is part of a key and so cannot be modified or marked as modified in EF Core

EF Core never updates a key value on a tracked entity. Stop copying the key from DTOs, use a unique index instead of an alternate key, and change a real key by inserting a new row and deleting the old one. Tested on EF Core 10.0.14.

2026-10-27 csharp dotnet performance

How to iterate over two collections in lockstep without heap allocations in C#

Enumerable.Zip allocates 144-208 bytes per call and runs about 10x slower than a plain loop. For arrays and lists, a for loop over two spans sliced to the same length is allocation-free and the fastest option; for foreach syntax, a small ref struct zip enumerator gets within 25% of it. Measured on .NET 10.0.10 and .NET 11 RC 3.

2026-10-27 polly resilience dotnet

Polly 8.8.1: The Circuit Breaker No Longer Keeps the First Caller's AsyncLocal Values Alive

Polly.Core 8.8.1 starts the circuit breaker's background loop under ExecutionContext.SuppressFlow, so a long-lived pipeline stops pinning the AsyncLocal values of whoever built it. A 15-line repro shows the leak on 8.8.0 and the fix on 8.8.1.

2026-10-26 dotnet csharp logging

How to use a different Serilog output template per log level from appsettings.json

outputTemplate is fixed per sink, so per-level formatting needs either an ExpressionTemplate with {#if @l ...} blocks or two Logger sub-loggers with ByIncludingOnly / ByExcluding filters. Both configured purely from appsettings.json, tested on Serilog 4.4, Serilog.Settings.Configuration 10.0.1 and Serilog.Expressions 5.0.

2026-10-23 dotnet playwright testing

Playwright .NET 1.64 adds Locator.Within(), and it is Locator chaining read backwards

Microsoft.Playwright 1.64 adds Locator.Within() so you can write 'this button, within that dialog'. A quick probe shows it builds exactly the same locator as parent.Locator(child), including per-parent Nth() resolution.

2026-10-22 comparison csharp dotnet

Lazy<T> vs LazyInitializer.EnsureInitialized vs double-checked locking in C#

Use Lazy<T> by default: it runs the factory once, caches exceptions, and its reads are too cheap to measure after initialization. Use LazyInitializer.EnsureInitialized when you lazily fill many fields or array slots and cannot afford an extra object per value. Hand-written double-checked locking is almost never worth it on .NET 10.

2026-10-21 mcp dotnet csharp

MCP C# SDK 2.3: McpClient.ServerInfo is now nullable, and your build may notice

ModelContextProtocol 2.3.0, released October 20, 2026, changes McpClient.ServerInfo from Implementation to Implementation? because 2026-07-28 servers may omit their identity from server/discover. Here is why, what breaks under warnings-as-errors, and the one-line fix.