// noescape hides a pointer from escape analysis.  noescape is// the identity function but escape analysis doesn't think the// output depends on the input.  noescape is inlined and currently// compiles down to zero instructions.// USE CAREFULLY!//go:nosplitfunc noescape(p unsafe.Pointer) unsafe.Pointer {x := uintptr(p)return unsafe.Pointer(x ^ 0)
}

package mainimport ("unsafe"
)type A struct {S *string
}func (f *A) String() string {return *f.S
}type ATrick struct {S unsafe.Pointer
}func (f *ATrick) String() string {return *(*string)(f.S)
}func NewA(s string) A {return A{S: &s}
}func NewATrick(s string) ATrick {return ATrick{S: noescape(unsafe.Pointer(&s))}
}func noescape(p unsafe.Pointer) unsafe.Pointer {x := uintptr(p)return unsafe.Pointer(x ^ 0)
}func main() {s := "hello"f1 := NewA(s)f2 := NewATrick(s)s1 := f1.String()s2 := f2.String()_ = s1 + s2
}

$go build -gcflags=-m main.go
# command-line-arguments
./main.go:11:6: can inline (*A).String
./main.go:19:6: can inline (*ATrick).String
./main.go:23:6: can inline NewA
./main.go:31:6: can inline noescape
./main.go:27:6: can inline NewATrick
./main.go:28:29: inlining call to noescape
./main.go:36:6: can inline main
./main.go:38:14: inlining call to NewA
./main.go:39:19: inlining call to NewATrick
./main.go:39:19: inlining call to noescape
./main.go:40:17: inlining call to (*A).String
./main.go:41:17: inlining call to (*ATrick).String
/var/folders/45/qx9lfw2s2zzgvhzg3mtzkwzc0000gn/T/go-build763863171/b001/_gomod_.go:6:6: can inline init.0
./main.go:11:7: leaking param: f to result ~r0 level=2
./main.go:19:7: leaking param: f to result ~r0 level=2
./main.go:24:16: &s escapes to heap
./main.go:23:13: moved to heap: s
./main.go:27:18: NewATrick s does not escape
./main.go:28:45: NewATrick &s does not escape
./main.go:31:15: noescape p does not escape
./main.go:38:14: main &s does not escape
./main.go:39:19: main &s does not escape
./main.go:40:10: main f1 does not escape
./main.go:41:10: main f2 does not escape
./main.go:42:9: main s1 + s2 does not escape

./main.go:24:16: &s escapes to heap    //这个是NewA中的，逃逸了
./main.go:23:13: moved to heap: s
./main.go:27:18: NewATrick s does not escape // NewATrick里的s的却没逃逸
./main.go:28:45: NewATrick &s does not escape