sync: get the size of sync.Map

[AlexStocks]

What version of Go are you using (go version)?

go 1.9 beta2

What did you expect to see?

If use map, I can get the size of it by len(map). Whatever, how can I get the size of sync.Map?

What did you see instead?

Add function: func (m *Map) Len() int

Maybe Map should have a member "size int64". Map can change its value in Store & LoadOrStore & Delete by using atomic.AddInt64. And then (m Map) Len() can return m.size to get Map's size.

[ALTree]

Thanks for the report.

This is an exact duplicate of #20680 (sync: add Map.Len method?), so I'm closing this thread in favour of the older one.

[AlexStocks]

okay