Issue #17316 has been updated by matz (Yukihiro Matsumoto). I understand the motivation, but the proposed "@||=" is unacceptable. Other suggestions were made, but I don't think any of them adequately express the intent. If there are no good operator name suggestions in the future, it would be better to explicitly use `defined?`. Matz. ---------------------------------------- Feature #17316: On memoization https://bugs.ruby-lang.org/issues/17316#change-114308 * Author: sawa (Tsuyoshi Sawada) * Status: Open ---------------------------------------- I have seen so many attempts to memoize a value in the form: ```ruby @foo ||= some_heavy_calculation(...) ``` improperly, i.e., even when the value can potentially be falsy. This practice is wide spread, and since in most cases memoization is about efficiency and it would not be critical if it does not work correctly, people do not seem to care so much about correcting the wrong usage. In such case, the correct form would be: ```ruby unless instance_variable_defined?(:@foo) @foo = some_heavy_calculation(...) end ``` but this looks too long, and perhaps that is keeping people away from using it. What about allowing `Kernel#instance_variable_set` to take a block instead of the second argument, in which case the assignment should be done only when the instance variable is not defined? ```ruby instance_variable_set(:@foo){some_heavy_calculation(...)} ``` Or, if that does not look right or seems to depart from the original usage of `instance_variable_set`, then what about having a new method? ```ruby memoize(:foo){some_heavy_calculation(...)} ``` -- https://bugs.ruby-lang.org/