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spec: type inference can't infer types for a generic union of functions #56975

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logandavies181 opened this issue Nov 29, 2022 · 2 comments
Open

spec: type inference can't infer types for a generic union of functions #56975

logandavies181 opened this issue Nov 29, 2022 · 2 comments
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generics Issue is related to generics NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Proposal-Hold TypeInference Issue is related to generic type inference
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@logandavies181
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What version of Go are you using (go version)?

$ go version
go version go1.19.3 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/vagrant/.cache/go-build"
GOENV="/home/vagrant/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/vagrant/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/vagrant/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.3"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/vagrant/scratch/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3122928231=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Try to use type inference for a generic interface whose only member is a union of functions

https://go.dev/play/p/uPJQhqqwMk0

What did you expect to see?

Program compiled successfully

What did you see instead?

./prog.go:12:5: cannot infer T (prog.go:7:10)

If the interface doesn't have a union then type inference works as expected:

https://go.dev/play/p/B-yRqxfvaK0
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Nov 29, 2022
@ianlancetaylor
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This is expected with the current language spec. There is no type inference rule that permits inferring the type argument for T in funcT[T].

@ianlancetaylor ianlancetaylor added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. generics Issue is related to generics TypeInference Issue is related to generic type inference and removed compiler/runtime Issues related to the Go compiler and/or runtime. labels Nov 29, 2022
@ianlancetaylor ianlancetaylor added this to the Backlog milestone Nov 29, 2022
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Nov 29, 2022
@mknyszek mknyszek changed the title cmd/compile: Type inference can't infer types for a generic union of functions spec: Type inference can't infer types for a generic union of functions Dec 7, 2022
@mknyszek mknyszek changed the title spec: Type inference can't infer types for a generic union of functions spec: type inference can't infer types for a generic union of functions Dec 7, 2022
@mknyszek mknyszek removed the compiler/runtime Issues related to the Go compiler and/or runtime. label Dec 7, 2022
@twmb twmb mentioned this issue Jan 5, 2023
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@griesemer
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Putting on hold because we also don't support calling the function in the generic code.

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@mknyszek @ianlancetaylor @griesemer @gopherbot @logandavies181