what is the scene to use mapaccess1_fat and mapaccess2_fat?
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xie cui
Dec 16, 2020, 1:39:55 AM12/16/20
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Axel Wagner
Dec 16, 2020, 8:41:36 AM12/16/20
to xie cui, golang-nuts
A little bit of guesswork, again (I'm not working on the compiler)
`mapaccess1` is obviously for map index expressions of the form `m[key]`, while `mapaccess2` is for assignments like `a, ok := m[key]`.
And AIUI the non-`_fat` versions are used if the value-type of the map is too large to fit into a pre-allocated array of zero-bytes. In that case, the runtime gets passed a separate pointer to a zero-value of that type to use as the default - I assume, in that case the compiler emits code to allocate (on the stack or the heap) zeroed memory of the appropriate size and passes that to `mapaccess1_fat`.
Hope that helps, even though I'm guessing :)
On Wed, Dec 16, 2020 at 7:40 AM xie cui <cuiw...@gmail.com> wrote:
https://github.com/golang/go/blob/master/src/runtime/map.go#L554
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