Move Spectre.Console.Cli to it's own package

src/Spectre.Console.Cli/FlagValue.cs

@@ -0,0 +1,55 @@
+namespace Spectre.Console.Cli;
+
+/// <summary>
+/// Implementation of a flag with an optional value.
+/// </summary>
+/// <typeparam name="T">The flag's element type.</typeparam>
+public sealed class FlagValue<T> : IFlagValue
+{
+    /// <summary>
+    /// Gets or sets a value indicating whether or not the flag was set or not.
+    /// </summary>
+    public bool IsSet { get; set; }
+
+#pragma warning disable CS8618 // Non-nullable field is uninitialized. Consider declaring as nullable.
+    /// <summary>
+    /// Gets or sets the flag's value.
+    /// </summary>
+    public T Value { get; set; }
+#pragma warning restore CS8618 // Non-nullable field is uninitialized. Consider declaring as nullable.
+
+    /// <inheritdoc/>
+    Type IFlagValue.Type => typeof(T);
+
+    /// <inheritdoc/>
+    object? IFlagValue.Value
+    {
+        get => Value;
+        set
+        {
+#pragma warning disable CS8601 // Possible null reference assignment.
+#pragma warning disable CS8600 // Converting null literal or possible null value to non-nullable type.
+            Value = (T)value;
+#pragma warning restore CS8600 // Converting null literal or possible null value to non-nullable type.
+#pragma warning restore CS8601 // Possible null reference assignment.
+        }
+    }
+
+    /// <inheritdoc/>
+    public override string ToString()
+    {
+        var flag = (IFlagValue)this;
+        if (flag.Value != null)
+        {
+            return string.Format(
+                CultureInfo.InvariantCulture,
+                "Set={0}, Value={1}",
+                IsSet,
+                flag.Value.ToString());
+        }
+
+        return string.Format(
+            CultureInfo.InvariantCulture,
+            "Set={0}", IsSet);
+    }
+}