Can unsafe.Sizeof be used with weak types / cgo

[Dave Cheney]

Consider the following program

% more t.go
package main

import (
"syscall"
"unsafe"
"fmt"
)

func main() {
fmt.Println(unsafe.Sizeof(syscall.Timeval))
}
% go run t.go
# command-line-arguments
./t.go:10: type syscall.Timeval is not an expression
./t.go:10: invalid expression unsafe.Sizeof(syscall.Timeval)

Is this a bug, or a limitation of cgo derived types ?

Cheers

Dave

[Rob 'Commander' Pike]

The function unsafe.Sizeof takes an expression as argument, not a
type. You want something like unsafe.Sizeof(syscall.TimeVal{})

-rob

[Dave Cheney]

Thank you for the explanation, I was confusing it with the C sizeof,
and probably using that incorrectly to boot.

Cheers

Dave

[Rob 'Commander' Pike]

To be pedantic, C sizeof doesn't operate on types either. The sizeof
operator applies to an expression or - this is the tricky bit - a type
cast.

thus
sizeof i
but also
sizeof(int)
but not
sizeof int

People think C sizeof is a function but it's an operator; the
expression sizeof(int) parses differently from the way most people
interpret it.

We're getting off topic.

-rob