On Sunday, February 25, 2018 at 7:38:22 PM UTC-5, Rob 'Commander' Pike
wrote:
>
> The main rule about unsafe is that your program might work or might not.
> There are no guarantees either way. That's why it's called 'unsafe' and why
> you shouldn't use it. Your program that 'works' today could break tomorrow.
>
ok, but, is there always an unsafe alternative/variant existing later?
>
> -rob
>
>
> On Mon, Feb 26, 2018 at 4:43 AM, Marvin Renich <mr...@renich.org
> <javascript:>> wrote:
>
>> * di...@veryhaha.com <javascript:> <di...@veryhaha.com <javascript:>>
>> [180225 11:37]:
>> > I think I get it.
>> > Because the above program tries to modify the constant (or program)
>> zone,
>> > which is not allowed.
>> > The following program works:
>>
>> But, note that the language spec does not guarantee it to work. The
>> compiler is free to recognize what that first line is doing and optimize
>> the assignment into a string in a R/O memory segment. The optimization
>> is legal because the compiler does not have to recognize the use of
>> unsafe to determine the programmer's intent to subvert the type system.
>>
>> > package main
>> >
>> > import "fmt"
>> > import "unsafe"
>> > import "reflect"
>> >
>> > func main() {
>> > s := string([]byte{'k', 'e', 'e', 'p'})
>> > hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
>> > byteSequence := (*byte)(unsafe.Pointer(hdr.Data))
>> > fmt.Println(string(*byteSequence)) // k
>> > *byteSequence = 'j' // crash here
>> > fmt.Println(s) // expect: jeep
>> > }
>>
>> ...Marvin
>>
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>
>
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