Type assertion with interface fails with "interface conversion: nil is not interface{}"
Author: tom93Created Apr 2, 2026Updated Apr 2, 2026
Update: The issue is with the conversion, not the type assertion; see comment.
The following program sample.go triggers an unexpected result
package main
func main() {
x := 42
y := interface{}(x)
println(y != nil)
println(y.(int) == 42)
println(y.(interface{}) != nil)
}Expected result
$ go run ./sample.go
true
true
trueGot
$ yaegi ./sample.go
true
true
sample.go:4:2: panic: main.main(...)
run: sample.go:8:10: interface conversion: nil is not interface{}
goroutine 1 [running]:
runtime/debug.Stack()
/home/user/go1.26.1/src/runtime/debug/stack.go:26 +0x5e
github.com/traefik/yaegi/interp.(*Interpreter).Execute.func1()
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/program.go:146 +0x79
panic({0xf341e0?, 0x202ee8228108?})
/home/user/go1.26.1/src/runtime/panic.go:860 +0x13a
github.com/traefik/yaegi/interp.runCfg.func1()
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/run.go:226 +0x1a5
panic({0xf341e0?, 0x202ee8228108?})
/home/user/go1.26.1/src/runtime/panic.go:860 +0x13a
github.com/traefik/yaegi/interp.typeAssert.func1(0x202ee823a0b0)
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/run.go:329 +0x4b4
github.com/traefik/yaegi/interp.runCfg(0x202ee81b0780, 0x202ee823a0b0, 0x4?, 0x0?)
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/run.go:234 +0x265
github.com/traefik/yaegi/interp.(*Interpreter).run(0x202ee7df1448, 0x202ee81a1cc0, 0x202ee7dda210?)
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/run.go:119 +0x36d
github.com/traefik/yaegi/interp.(*Interpreter).Execute(0x202ee7df1448, 0x202ee8219650)
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/program.go:172 +0x225
github.com/traefik/yaegi/interp.(*Interpreter).eval(0x202ee7df1448, {0x202ee7dbb3b0?, 0x88?}, {0x7ffc2cf0490e?, 0x202ee8103b00?}, 0x90?)
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/interp.go:563 +0x55
github.com/traefik/yaegi/interp.(*Interpreter).EvalPath(0x202ee7df1448, {0x7ffc2cf0490e, 0x9})
/home/user/go/pkg/mod/github.com/traefik/[email protected]/interp/interp.go:512 +0xa6
main.runFile(0x202ee7df1448, {0x7ffc2cf0490e, 0x9}, 0x0)
/home/user/go/pkg/mod/github.com/traefik/[email protected]/cmd/yaegi/run.go:153 +0xd8
main.run({0x202ee7d3c150, 0x1, 0x1})
/home/user/go/pkg/mod/github.com/traefik/[email protected]/cmd/yaegi/run.go:116 +0x998
main.main()
/home/user/go/pkg/mod/github.com/traefik/[email protected]/cmd/yaegi/yaegi.go:144 +0x2d7Yaegi Version
v0.16.1 (yeagi version outputs "devel")
Additional Notes
Hi, this is a very cool and ambitious project, but please consider weakening the claim "Complete support of Go specification" in the feature list in the README.
Source: traefik/yaegi