POLA fetch

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(Proposals: note need to provide default-value behavior)
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== Proposals ==
== Proposals ==
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* Make the second argument usually an ejector. Ejectors do not return values and are robust against being invoked multiple times; if some other sort of object is being used, its author is more likely to consider the multiple invocation issue. --[[User:Kevin Reid|Kevin Reid]] 11:25, 12 April 2008 (CDT)
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* Make the second argument usually an ejector. Ejectors do not return values and are robust against being invoked multiple times; if some other sort of object is being used, its author is more likely to consider the multiple invocation issue. If we do this, then utilities should be provided for default-value behavior. --[[User:Kevin Reid|Kevin Reid]] 11:25, 12 April 2008 (CDT)
[[Category:Unresolved design issues]]
[[Category:Unresolved design issues]]

Revision as of 16:35, 12 April 2008

to fetch(key, absentThunk)

The fetch/2 protocol for collections does not obey POLA:

  • The collection gets access to the value of absentThunk.
  • The collection may invoke absentThunk and yet return something else.
  • The collection may invoke absentThunk more than once, or after fetch returns.

Proposals

  • Make the second argument usually an ejector. Ejectors do not return values and are robust against being invoked multiple times; if some other sort of object is being used, its author is more likely to consider the multiple invocation issue. If we do this, then utilities should be provided for default-value behavior. --Kevin Reid 11:25, 12 April 2008 (CDT)
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