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/**
* Copyright (c) David Miller. All rights reserved.
* The use and distribution terms for this software are covered by the
* Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
* which can be found in the file epl-v10.html at the root of this distribution.
* By using this software in any fashion, you are agreeing to be bound by
* the terms of this license.
* You must not remove this notice, or any other, from this software.
**/
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.CompilerServices;
namespace clojure.lang
{
/// <summary>
/// Implements a delay of a function call.
/// </summary>
public class Delay : IDeref
{
#region Data
/// <summary>
/// The value, after it has been computed.
/// </summary>
object _val;
/// <summary>
/// The function being delayed.
/// </summary>
IFn _fn;
#endregion
#region C-tors
/// <summary>
/// Construct a delay for a function.
/// </summary>
/// <param name="fn">The function to delay.</param>
public Delay(IFn fn)
{
_fn = fn;
_val = null;
}
#endregion
#region Delay operations
/// <summary>
/// Force a delay (or identity if not a delay).
/// </summary>
/// <param name="x">The object to force.</param>
/// <returns>The computed valued (if a delay); the object itself (if not a delay).</returns>
public static object force(object x)
{
return (x is Delay)
? ((Delay)x).deref()
: x;
}
#endregion
#region IDeref Members
/// <summary>
/// Get the value.
/// </summary>
/// <returns>The value</returns>
/// <remarks>Forces the computation if it has not happened yet.</remarks>
[MethodImpl(MethodImplOptions.Synchronized)]
public object deref()
{
if (_fn != null)
{
_val = _fn.invoke();
_fn = null;
}
return _val;
}
#endregion
}
}
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