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Function with optional default argument cannot cache results

• To: mathgroup at smc.vnet.net
• Subject: [mg130670] Function with optional default argument cannot cache results
• From: Dan O'Brien <danobrie at gmail.com>
• Date: Wed, 1 May 2013 03:37:54 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• Delivered-to: l-mathgroup@wolfram.com
• Delivered-to: mathgroup-outx@smc.vnet.net
• Delivered-to: mathgroup-newsendx@smc.vnet.net

Is there a discussion somewhere on why this is?

In[1]:= $Version
f[x_, y_: 2] := f[x, y] = {Pause[1], x, y}
f[1, 2] // AbsoluteTiming
f[1, 2] // AbsoluteTiming
f[1] // AbsoluteTiming
f[1] // AbsoluteTiming

Out[1]= "9.0 for Microsoft Windows (64-bit) (January 25, 2013)"

Out[3]= {1.014002, {Null, 1, 2}}

Out[4]= {0., {Null, 1, 2}}

Out[5]= {1.029602, {Null, 1, 2}}

Out[6]= {1.014002, {Null, 1, 2}}

• Follow-Ups:
  • Re: Function with optional default argument cannot cache results
    • From: Sseziwa Mukasa <mukasa@gmail.com>
  • Re: Function with optional default argument cannot cache
    • From: Waclaw Kusnierczyk <waku@idi.ntnu.no>