尝试删除临时符号时出现意外的删除::rmnsm 错误

发布于 2024-11-02 08:43:09 字数 531 浏览 4 评论 0原文

美好的一天，

请考虑以下事项：

In[1]:= HoldComplete[With[{line=a},Null]]
Names["`*"]
Attributes/@Names["`*"]
Remove/@Names["`*"]
Out[1]= HoldComplete[With[{line=a},Null]]
Out[2]= {a,line,line$}
Out[3]= {{},{},{Temporary}}
During evaluation of In[1]:= Remove::rmnsm: There are no symbols matching
"line$". >>
Out[4]= {Null,Null,Null}

尽管是临时的，但可以看到出现 Remove::rmnsm 消息 Symbol line$ 在那一刻仍然存在。为什么会出现这种情况？

PS 我正在使用 Mathematica 7.01。在 v.5.2 中，此消息不会出现。

原文

Good day,

Consider the following:

In[1]:= HoldComplete[With[{line=a},Null]]
Names["`*"]
Attributes/@Names["`*"]
Remove/@Names["`*"]
Out[1]= HoldComplete[With[{line=a},Null]]
Out[2]= {a,line,line$}
Out[3]= {{},{},{Temporary}}
During evaluation of In[1]:= Remove::rmnsm: There are no symbols matching
"line$". >>
Out[4]= {Null,Null,Null}

One can see that Remove::rmnsm message appear although the temporary
Symbol line$ still exists up the that moment. Why this happens?

P.S. I am using Mathematica 7.01. In v.5.2 this message does not appear.

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摇划花蜜的午后 2024-11-09 08:43:09

我认为发生的情况是，当您删除符号 line 时，就没有对临时变量 line$ 的进一步引用，因此它会自动删除。

In[1]:= HoldComplete[With[{line=a},Null]]
        Names["`*"]
        Attributes/@Names["`*"]
Out[1]= HoldComplete[With[{line=a},Null]]
Out[2]= {a,line,line$}
Out[3]= {{},{},{Temporary}}

In[4]:= Remove["line"]

In[5]:= Names["`*"]
Out[5]= {a}

这已在 Mma v8 中进行了测试。那么自 v5 以来，引用计数（或本地化的实现）可能略有变化？

请注意，如果您尝试先删除临时符号，您会收到一条信息丰富的警告：

In[6]:= HoldComplete[With[{line=a},Null]]
        Names["`*"]
        Attributes/@Names["`*"]
        Remove/@Reverse@Names["`*"]
Out[6]= HoldComplete[With[{line=a},Null]]
Out[7]= {a,line,line$}
Out[8]= {{},{},{Temporary}}
During evaluation of In[6]:= Remove::relex: Cannot remove lexical symbol 
   line$ except automatically (when line is removed). >>
Out[9]= {Null,Null,Null}

I think what is happening is when you remove the Symbol line then there are no further references to the temporary variable line$ and so it is automagically removed.

In[1]:= HoldComplete[With[{line=a},Null]]
        Names["`*"]
        Attributes/@Names["`*"]
Out[1]= HoldComplete[With[{line=a},Null]]
Out[2]= {a,line,line$}
Out[3]= {{},{},{Temporary}}

In[4]:= Remove["line"]

In[5]:= Names["`*"]
Out[5]= {a}

This was tested in Mma v8. So maybe the reference counting (or the implementation of localization) has changed slightly since v5?

Note that if you try to remove the temporary symbol first, you get quite an informative warning:

In[6]:= HoldComplete[With[{line=a},Null]]
        Names["`*"]
        Attributes/@Names["`*"]
        Remove/@Reverse@Names["`*"]
Out[6]= HoldComplete[With[{line=a},Null]]
Out[7]= {a,line,line$}
Out[8]= {{},{},{Temporary}}
During evaluation of In[6]:= Remove::relex: Cannot remove lexical symbol 
   line$ except automatically (when line is removed). >>
Out[9]= {Null,Null,Null}

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