task/dict extension

src/DictionaryExtensions.cs

@@ -1,5 +1,8 @@
+using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
+using System.Threading.Tasks;
 
 /// <summary>
 /// Dictionary Extensions
@@ -31,14 +34,19 @@ public static class DictionaryExtensions
         this IEnumerable<IEnumerable<KeyValuePair<TKey, TValue>>> @this) where TKey : notnull
     {
         var result = new Dictionary<TKey, TValue>();
-        foreach (var (key, value) in @this.SelectMany())
-        {
-            if (result.ContainsKey(key))
-                result[key] = value;
-            else
-                result.Add(key, value);
-        }
-
+        foreach (var (key, value) in @this.SelectMany()) result[key] = value;
         return result;
     }
+
+    /// <summary>
+    /// Return a task waiting for each key on the dictionary
+    /// </summary>
+    [SuppressMessage("AsyncUsage",
+        "AsyncFixer02:Long-running or blocking operations inside an async method")]
+    public static async Task<IDictionary<TKey, TValue>> WhenAll<TKey, TValue>(
+        this IDictionary<TKey, Task<TValue>> @this) where TKey : notnull
+    {
+        await Task.WhenAll(@this.Values).ConfigureAwait(false);
+        return @this.ToDictionary(x => x.Key, x => x.Value.Result);
+    }
 }