Sharing some utilities from real-world code

[nadako]

Sometimes (mostly for the purpose of animations) we want to differentiate between initial binding and update callbacks, as well as having previous value at hand. This can be achieved by some basic extension methods that wrap the callbacks and provide additional information.

using System;
using TinkState;

static class ObservableExtensions
{
    public static IDisposable BindWithInitial<T>(this Observable<T> observable, Action<T, bool> callback)
    {
        var initial = true;
        return observable.Bind(value =>
        {
            if (initial)
            {
                initial = false;
                callback(value, true);
            }
            else
            {
                callback(value, false);
            }
        });
    }

    // this is not very elegant and may cause memory "leak" if T is something that holds a lot of memory...
    public static IDisposable BindWithPrevious<T>(this Observable<T> observable, Action<T, T> callback)
    {
        var previous = observable.Value;
        return observable.Bind(value =>
        {
            var old = previous;
            previous = value;
            callback(value, old);
        });
    }
}