sync: Map.Delete to return deleted value

[localvar]

I need to know if an item is actually deleted when call Delete of sync.Map, but the function returns nothing currently.

Is it possible for it to return the deleted value and/or a bool to indicate whether something is really deleted?

Thanks.

[agnivade]

It is not possible to do that without breaking Go1 compatibility. I assume that you don't want to make an extra .Load call to check whether the element is present in the map or not ?

[agnivade]

/cc @bcmills

[localvar]

@agnivade, thanks for the reply. However, I don't think an extra .Load call works, because the item could be deleted in another go-routine between my call to .Load and .Delete.

I have little knowledge about Go1 compatibility, but in my understanding, add return value to .Delete won't break any existing code, because it currently returns nothing.

[davecheney]

@localvar 'fraid not, the current interpretation of the Go 1 contract assumes that someone has assigned a method as a function; eg

var m sync.Map
var del = m.Delete

Changing the signature of sync.Map.Delete could break code like this, depending on how del is used, hence this type of proposal is not acceptable under the Go1 contract.

[davecheney]

Duplicate of #23547 and closing as #23547 states that this change cannot be accepted.

[agnivade]

Ah I was pretty sure this was raised before but could not find anything when I searched. Thanks.

[localvar]

Is adding a new function (for an ugly example: Delete2) acceptable?

I checked the source code and find the internal entry.delete does have a return value.