/// <summary>
/// Returns the descendant at a particular location in <paramref name="value"/>
/// </summary>
/// <param name="rewriter">The rewriter</param>
/// <param name="value">The rewritable tree type</param>
/// <param name="path">The route to take to find the descendant</param>
/// <exception cref="InvalidOperationException">
/// Thrown if <paramref name="path"/> leads off the edge of the tree
/// </exception>
/// <returns>The descendant found by following the directions in <paramref name="path"/></returns>
public static T DescendantAt <T>(this IRewriter <T> rewriter, IEnumerable <Direction> path, T value)
{
if (rewriter == null)
{
throw new ArgumentNullException(nameof(rewriter));
}
if (path == null)
{
throw new ArgumentNullException(nameof(path));
}
var cursor = rewriter.Cursor(value);
cursor.Follow(path);
return(cursor.Focus);
}
/// <summary>
/// Apply an asynchronous function at a particular location in <paramref name="value"/>
/// </summary>
/// <param name="rewriter">The rewriter</param>
/// <param name="value">The rewritable tree type</param>
/// <param name="path">The route to take to find the descendant</param>
/// <param name="transformer">An asynchronous function to calculate a replacement for the descendant</param>
/// <exception cref="InvalidOperationException">
/// Thrown if <paramref name="path"/> leads off the edge of the tree
/// </exception>
/// <returns>
/// A copy of <paramref name="value"/> with the result of <paramref name="transformer"/> placed at the location indicated by <paramref name="path"/>
/// </returns>
/// <remarks>This method is not available on platforms which do not support <see cref="ValueTask"/>.</remarks>
public static async ValueTask <T> RewriteDescendantAt <T>(this IRewriter <T> rewriter, IEnumerable <Direction> path, Func <T, ValueTask <T> > transformer, T value)
{
if (rewriter == null)
{
throw new ArgumentNullException(nameof(rewriter));
}
if (path == null)
{
throw new ArgumentNullException(nameof(path));
}
if (transformer == null)
{
throw new ArgumentNullException(nameof(transformer));
}
var cursor = rewriter.Cursor(value);
cursor.Follow(path);
cursor.Focus = await transformer(cursor.Focus).ConfigureAwait(false);
cursor.Top();
return(cursor.Focus);
}