feat: introduced SelectComponent and SelectComponentOrDefault

src/Gallium/SelectComponentExtensions.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Collections.Generic;
+
+namespace Gallium;
+
+/// <summary>
+/// Extension methods for selecting components from a list.
+/// </summary>
+public static class SelectComponentExtensions
+{
+    /// <summary>
+    /// Retrieves a component from an entity and return it. If the entity does not have
+    /// the component, it will be
+    /// filtered out.
+    /// </summary>
+    /// <param name="entities">The entities to process.</param>
+    /// <typeparam name="T1">The component type being searched.</typeparam>
+    /// <returns>A sequence of T1.</returns>
+    public static IEnumerable<T1> SelectComponent<T1>(this IEnumerable<Entity> entities)
+    {
+        foreach (Entity entity in entities)
+        {
+            if (entity.TryGet(out T1 v1))
+            {
+                yield return v1;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Retrieves a component from an entity and return it. If the entity does not have
+    /// the component, it will be filtered out.
+    /// </summary>
+    /// <param name="entities">The entities to process.</param>
+    /// <param name="t1">The component type being searched.</param>
+    /// <returns>A sequence of T1.</returns>
+    public static IEnumerable<object> SelectComponent(
+        IEnumerable<Entity> entities,
+        Type t1)
+    {
+        foreach (Entity entity in entities)
+        {
+            if (entity.Has(t1))
+            {
+                yield return entity.Get<object>(t1);
+            }
+        }
+    }
+}

src/Gallium/SelectComponentOrDefaultExtensions.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Collections.Generic;
+
+namespace Gallium;
+
+/// <summary>
+/// Extension methods for selecting components from a list.
+/// </summary>
+public static class SelectComponentOrDefaultExtensions
+{
+    /// <summary>
+    /// Retrieves a component from an entity and return it. If the entity does not have
+    /// the component, then null will be returned.
+    /// </summary>
+    /// <param name="entities">The entities to process.</param>
+    /// <param name="t1">The component type being searched.</param>
+    /// <returns>A sequence of T1 or nulls.</returns>
+    public static IEnumerable<object?> SelectComponent(
+        IEnumerable<Entity> entities,
+        Type t1)
+    {
+        foreach (Entity entity in entities)
+        {
+            if (entity.Has(t1))
+            {
+                yield return entity.Get<object>(t1);
+            }
+
+            yield return null;
+        }
+    }
+
+    /// <summary>
+    /// Retrieves a component from an entity and return it. If the entity does not have
+    /// the component, then the default value will be returned.
+    /// </summary>
+    /// <param name="entities">The entities to process.</param>
+    /// <typeparam name="T1">The component type being searched.</typeparam>
+    /// <returns>A sequence of T1.</returns>
+    public static IEnumerable<T1?> SelectComponentOrDefault<T1>(this IEnumerable<Entity> entities)
+    {
+        foreach (Entity entity in entities)
+        {
+            if (entity.TryGet(out T1 v1))
+            {
+                yield return v1;
+            }
+
+            yield return default;
+        }
+    }
+}