Why should you care?

ShopNest map pins for thousands of stores reuse the same icon/style objects instead of copying them.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public sealed class PinStyle
{
    public string Icon { get; }
    public string Color { get; }
    public PinStyle(string icon, string color) { Icon = icon; Color = color; }
}
public static class PinStyleFactory
{
    private static readonly Dictionary<string, PinStyle> Cache = new();
    public static PinStyle Get(string icon, string color)
    {
        var key = icon + ":" + color;
        if (!Cache.TryGetValue(key, out var style))
            Cache[key] = style = new PinStyle(icon, color);
        return style;
    }
}
public readonly record struct StorePin(string StoreId, double Lat, double Lng, PinStyle Style);

var style = PinStyleFactory.Get("shop", "blue");
var pins = new[] { new StorePin("s1", 18.5, 73.8, style), new StorePin("s2", 18.6, 73.9, style) };
Console.WriteLine(ReferenceEquals(pins[0].Style, pins[1].Style));

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• PinStyle is intrinsic/shared; store id and coordinates are extrinsic.
• Factory caches styles.
• ReferenceEquals is true for the shared style.

Practice next

1. Create two pins sharing a style; confirm ReferenceEquals.
2. Request a red style and see a second cache entry.
3. Keep PinStyle immutable.
4. Print Cache.Count after several Get calls.
5. Add a size field to PinStyle.

Remember

Share immutable intrinsic state. Pass extrinsic per use. Cache carefully.

ShopNest store-map pins

Map renders thousands of pins with few styles.

Outcome: Memory stays flat as store count grows.