/// <summary>
/// Accept a <see cref="QueryNodeVisitor{T}"/> that walks the tree of <see cref="QueryNode"/>s.
/// </summary>
/// <typeparam name="TResult">The type returned by the visitor.</typeparam>
/// <param name="visitor">A visitor implementation used to walk the <see cref="QueryNode"/> tree.</param>
/// <returns>An object whose type is determined by the type parameter <typeparamref name="TResult"/>.</returns>
public abstract TResult Accept <TResult>(QueryNodeVisitor <TResult> visitor);
/// <summary>
/// Accept a <see cref="QueryNodeVisitor{T}"/> that walks the tree of <see cref="QueryNode"/>s.
/// </summary>
/// <typeparam name="TResult">The type returned by the visitor.</typeparam>
/// <param name="visitor">A visitor implementation used to walk the <see cref="QueryNode"/> tree.</param>
/// <returns>An object whose type is determined by the type parameter <typeparamref name="TResult"/>.</returns>
/// <exception cref="System.ArgumentNullException">Throws if the <paramref name="visitor"/> argument is null.</exception>
public override TResult Accept <TResult>(QueryNodeVisitor <TResult> visitor)
{
Check.IsNotNull(visitor, nameof(visitor));
return(visitor.Visit(this));
}