Generic type does not match when the type should match

[intangere]

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

$ go version
go version go1.21.5 linux/amd64

Does this issue reproduce with the latest release?

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

go env Output

$ go env
GO111MODULE='on'
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/phi/.cache/go-build'
GOENV='/home/phi/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/phi/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/phi/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/lib/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/lib/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.5'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3804273348=/tmp/go-build -gno-record-gcc-switches'
uname -sr: Linux 6.1.68-1-MANJARO
LSB Version:	n/a
Distributor ID:	ManjaroLinux
Description:	Manjaro Linux
Release:	23.1.0
Codename:	Vulcan
/usr/lib/libc.so.6: GNU C Library (GNU libc) stable release version 2.38.
gdb --version: GNU gdb (GDB) 13.2

What did you do?

package main

import "fmt"

func CallOneArg[T1 any](f func(T1), args []any) {
	f(args[0].(T1))
}

func CallTwoArgs[T1, T2 any](f func(T1, T2), args []any) {
	f(args[0].(T1), args[1].(T2))
}

func Caller[F any](f F, args []any) {
	switch len(args) {
		case 1:
			CallOneArg(f, args) // type F of f does not match func(T1) (cannot infer T1)
		case 2:
			CallTwoArgs(f, args) // type F of f does not match func(T1, T2) (cannot infer T1 and T2)
	}
}

func MyFunc1(arg1 string) {
	fmt.Println(arg1)
}

func MyFunc2(arg1 string, arg2 string) {
	fmt.Println(arg1, arg2)
}

func main() {
	Caller(MyFunc1, []any{"Hello World!"})
	Caller(MyFunc2, []any{"Hello World!", "Bye World!"})
}

What did you expect to see?

The program to compile because type F does match func(T1) in the first case, and func(T1, T2) in the second case.
If you explicitly type assert such as CallOneArg(any(f).(func(string)) and CallTwoArgs(any(f).(func(string, string)), args) it will compile, but that defeats the entire purpose of the code. I'm not sure if this is a bug or a case of type inference not being implemented but it makes sense for this to work.

What did you see instead?

./compile.go:16:15: type F of f does not match func(T1) (cannot infer T1)
./compile.go:18:16: type F of f does not match func(T1, T2) (cannot infer T1 and T2)

[gabyhelp]

Related Issues

• cmd/compile: "type does not match inferred type" even though it compiles when the inferred type is explicitly provided as type argument #53389 (closed)
• spec: function type inference ignores type parameter constraints #50272 (closed)
• spec: interfaces that have different-size method sets never unify (but they possibly could) #57192 (closed)
• generics: Generic function not accepting nil as an argument #51729 (closed)
• affected/package: #52787 (closed)
• cmd/compile: constraint type inference for generic types is not implemented #54469 (closed)
• spec: type inference can't infer types for a generic union of functions #56975
• cmd/compile: specific type for generic struct type in recevier #62030 (closed)
• cmd/compile, go/types: recursive type matching regression #48695 (closed)
• go/types, types2: type inference fails if inferred type is generic function #59953 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

I believe the compiler is correct, there is no set of type parameters you can explicitly pass to make the code compile as is.
F any is not a sufficient constraint for it to be used as a function, F could be any other value

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