The Go programming language
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Robert Griesemer 96c94c2c83 cmd/compile/internal/types2: slightly relax notion of structural type
If we have all channel types in a constraint, there is no structural type
if they don't all have the same channel direction (and identical element
types, of course). By allowing different channel types for the purposes of
the structural type, as long as there is not a send-only _and_ a receive-
only channel in the type set, we make it possible to find a useful, if
restricted by channel direction, structural type where before there was
none.

So if we have unrestricted and send-only channels, the structural type is
the send-only channel, and vice versa.

For all operations on channels that rely on a structural type, it's always
ok to have an unrestricted channel, so this is not affecting their behavior.
But it makes those operations more flexible in the presence of type parameters
containing mixed channel types.

For constraint type inference, where we currently may not infer a channel
at all, this change allows us to infer a more restricted channel (send- or
receive-only). If the inferred channel type is a valid type argument we win;
if not we haven't lost anything.

Use structuralType for send and receive operations and adjust related
error messages (the error message that change are the ones involving
type parameters, so historic error messages are preserved).

Fixes #45920.

Change-Id: If3a64d29c37e7734d3163df330f8b02dd032bc60
Reviewed-on: https://go-review.googlesource.com/c/go/+/363075
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
2021-11-10 21:59:23 +00:00
.github .github: update IRC server 2021-09-30 19:56:27 +00:00
api syscall: migrate new UDP send/recv API to internal/syscall/unix 2021-11-03 21:45:33 +00:00
doc doc: make a copy of the latest Go 1.17 spec 2021-11-10 05:08:25 +00:00
lib/time lib/time: fix RFC 6557 url 2021-08-15 02:18:46 +00:00
misc all: add support for c-archive and c-shared on linux/riscv64 2021-11-03 09:23:34 +00:00
src cmd/compile/internal/types2: slightly relax notion of structural type 2021-11-10 21:59:23 +00:00
test cmd/compile: don't do Resolve on OKEY identifiers during import 2021-11-10 21:53:03 +00:00
.gitattributes all: treat all files as binary, but check in .bat with CRLF 2020-06-08 15:31:43 +00:00
.gitignore internal/buildcfg: move build configuration out of cmd/internal/objabi 2021-04-16 19:20:53 +00:00
AUTHORS A+C: add Leonard Wang (individual CLA) 2021-11-02 06:25:39 +00:00
CONTRIBUTING.md all: restore changes from faulty merge/revert 2018-02-12 20:13:59 +00:00
CONTRIBUTORS A+C: add Leonard Wang (individual CLA) 2021-11-02 06:25:39 +00:00
LICENSE
PATENTS
README.md README.md: update contribute URL 2021-09-30 13:33:21 +00:00
SECURITY.md SECURITY.md: update go versions 2019-09-26 15:34:57 +00:00
codereview.cfg codereview.cfg: add codereview.cfg for master branch 2021-02-19 18:44:53 +00:00

README.md

The Go Programming Language

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