[GROOVY-7802] MapWithDefault should be able to be configured to not store its default value

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.6
• Fix Version/s: 4.0.1
• Component/s: groovy-jdk
• Flags: Patch
• Assignee: Paul King
• Reporter: Pap Lőrinc
• Created: 28/Mar/16 12:03
• Updated: 16/Apr/23 16:15
• Resolved: 26/Feb/22 11:27

Description

As described in https://github.com/apache/groovy/pull/267, a Groovy map with a default value stores all the accessed elements, even if they weren't added explicitly, just queried.

In certain algorithms (e.g. https://github.com/careercup/CtCI-6th-Edition-Groovy/blob/d116d65469bdf17d1e215e89f3e76ac3a97660a9/src/main/groovy/Ch04_TreesAndGraphs/_04_12_PathsWithSum.groovy#L21) the complexity would automatically be reduced, if default values would be deleted (i.e. a default of 0 that is incremented and decremented in a recursive algorithm).

Topics of discussion:

• Currently a `getAt` will `add` also, therefore `containsKey` isn't the same as `getAt(...) != null`
• After the change `keySet()/entrySet()` wouldn't include default values

I proposed alternatives:

• `removeIfDefault(Object)` // removes current key, if value is equal to default
• `consolidate()` // removes all default values
• constructor parameter `STORE_DEFAULT storeDefaultValues = STORE_DEFAULT.FALSE`, or maybe with a `boolean`, though I find primitive parameters confusing

others:

• `containsKey` should always return `true`, or throw an exception, since its behavior is inconsistent

Waiting for your thoughts

Issue Links

• relates to: GROOVY-9848 Allow membership operator to work on maps