....{property: {subProperty: pattern}}....

....{property.subProperty: pattern}....

public record TestRec(string name, string surname);

string TakeFourSymbols(TestRec obj) => obj switch
{
    TestRec { name: {Length: > 4} } rec => rec.name.Substring(0,4),
    // ...
};

string TakeFourSymbols(TestRec obj) => obj switch
{
    TestRec { name.Length: > 4 } rec => rec.name.Substring(0,4),
    // ...
};

const string constStrFirst = "FirstStr";
const string summaryConstStr = $"SecondStr {constStrFirst}";

const char a = 'a';
const string constStrFirst = "FirstStr";
const string summaryConstStr = $"SecondStr {constStrFirst} {a}";

// Error CS0133
// The expression being assigned to
// 'summaryConstStr' must be constant

public void Configure(IApplicationBuilder app, IHostingEnvironment env)

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)

using Microsoft.Extensions.Hosting;

using System;
using System.Threading;
using System.Threading.Tasks;
 
namespace MyApp
{
    public class AsyncLock : IDisposable
    {
        private SemaphoreSlim _semaphoreSlim = new SemaphoreSlim(1, 1);
 
        public async Task<AsyncLock> LockAsync()
        {
            await _semaphoreSlim.WaitAsync();
            return this;
        }
 
        public void Dispose()
        {
            _semaphoreSlim.Release();
        }
    }
}

private static readonly AsyncLock _mutex = new AsyncLock();
 
using(await _mutex.LockAsync())
{
    // Critical section... You can await here!
}