Hey, All:
I have made a little testing about interface assignment and searched
the source code about interface runtime functions like convI2I, and notice
that
there are two situations where data may be copied or not:
(1) data not copied: assign another* interface type* variable to the
targeted interface variable
(2) data copied and memory allocated: assign another *not interface
type *variable to the targeted interface variable
I wonder are there any special reasons for that?
Thanks in advance! following is my simple testing code and debug info
// interface.go
package main
import "fmt"
type Data struct {
n int
}
func main() {
d := Data{10}
fmt.Printf("address of d: %p\n", &d)
// assign not interface type variable to interface variable
// d will be copied
var i1 interface{} = d
// assign interface type variable to interface variable
// the data of i1 will directly assigned to i2.data and will not be copied
var i2 interface{} = i1
fmt.Println(d)
fmt.Println(i1)
fmt.Println(i2)
}
// build without optimization and inline
go build -gcflags "-N -l" interface.go
// the data address of i1 and i2 are the same
(gdb) info locals
&d = 0xc420074168
i2 = {_type = 0x492e00, data = 0xc4200741a0}
i1 = {_type = 0x492e00, data = 0xc4200741a0}
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