[matti@babylon trace (master)] % gomobile version
gomobile version unknown: binary is out of date, re-install it

$ go get golang.org/x/mobile/cmd/gomobile
$ gomobile init

go get -u cloud.google.com/go/trace
cd ~/go/src/cloud.google.com/go/trace
gomobile bind -target ios -o /tmp/Cloudtrace.framework

gomobile: darwin-arm: go build -tags ios -buildmode=c-archive -o /var/folders/jw/jrh0fgfn42ndjty5zpbsv8p00000gn/T/gomobile-work-736257513/trace-arm.a gobind failed: exit status 2
# gobind
/var/folders/jw/jrh0fgfn42ndjty5zpbsv8p00000gn/T/gomobile-work-736257513/src/gobind/go_tracemain.go:53: cannot use (*proxytrace_SamplingPolicy)(_param_p0_ref) (type *proxytrace_SamplingPolicy) as type "cloud.google.com/go/trace".SamplingPolicy in assignment:
	*proxytrace_SamplingPolicy does not implement "cloud.google.com/go/trace".SamplingPolicy (missing Sample method)

type SamplingPolicy interface {
        // Sample returns a Decision.
        // If Trace is false in the returned Decision, then the Decision should be
        // the zero value.
        Sample(p Parameters) Decision
}

// Parameters contains the values passed to a SamplingPolicy's Sample method.
type Parameters struct {
        HasTraceHeader bool // whether the incoming request has a valid X-Cloud-Trace-Context header.
}

// Decision is the value returned by a call to a SamplingPolicy's Sample method.
type Decision struct {
        Trace  bool    // Whether to trace the request.
        Sample bool    // Whether the trace is included in the random sample.
        Policy string  // Name of the sampling policy.
        Weight float64 // Sample weight to be used in statistical calculations.
}