Issue #20818 has been reported by furunkel (Julian Aron Prenner). ---------------------------------------- Feature #20818: Allow passing a block to Hash#store (to update current value) https://bugs.ruby-lang.org/issues/20818 * Author: furunkel (Julian Aron Prenner) * Status: Open ---------------------------------------- I would like to propose a block form for `Hash#store`. In addition to passing a value, it should also be allowed to pass a block. If passed a block instead of a value, the block is called with the current value or, if unset, the hash's default value; the block's return value will be the value that is stored. This is similar to e.g., `computeIfPresent`/`computeIfAbsent` in Java (I think). I can think of several situations where this would be useful, in particular for caches and counters. For instance: ```ruby counts = {} elements.each do |element| counts.store(element){ (_1 || 0) + element.weight} end ``` or even more elegant with a default value: ```ruby counts = {} counts.default = 0 elements.each do |element| counts.store(element){ _1 + element.weight} end ``` Moreover, using the block form we should be able to do operations such as `h[k] ||= x`, `h[k] -= x`, `h[k] += x`, or more generally `h[k] = f(h[k])`, with a single "hashing round-trip". If I'm not mistaken, currently these involve two separate calls to `#[]` and `#[]=` (with two calls to `#hash`?). Finally, this makes `#store` a proper dual of `#fetch` which, similarly, can be passed a block. I have an experimental implementation of this (GitHub PR) at: https://github.com/ruby/ruby/pull/11956 -- https://bugs.ruby-lang.org/