#unsafe package

146 messages · Page 1 of 1 (latest)

acoustic star
# 
package main

import "fmt"
import "unsafe"

func main() {
    var myname string = "hello world"

    ptr := (*uint8)(unsafe.Add(unsafe.Pointer(&myname), 8))

    *ptr = 1


    fmt.Println("the value :",myname)
    fmt.Println("the size  :",unsafe.Sizeof(myname))

}

``8`` is the pointer ``size`` in this case we are dealing with ``ascii`` english characters we should keep the pointer size ``8`` and lastly we did type conversion because we are returning a pointer that has no type so we need to cast the pointer and give it a type but what confuses me ``unsafe.Add`` this meant to do ``slicing`` as i worked with a little bit and from what i understood !!
sweet iris
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this code is illegal, strings are immutable

acoustic star
sweet iris
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I don't understand the description

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but fwiw the code is wrong so, probably

acoustic star
sweet iris
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any of it

acoustic star
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i have mentioned that the number 8 is the size of the pointer

sweet iris
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that's not totally correct

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but most of the time, yes

acoustic star
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what i understand from you

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depending on the context

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is that what you are trying to say ?

sweet iris
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it depends on the target architecture

acoustic star
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i see

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is the length of the pointer should equal to the type it's beencasted to ?

sweet iris
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I don't understand what that means, pointers don't have a length

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the size of a pointer value is architecture dependent

acoustic star
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i know but you set the size of the pointer

sweet iris
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are you referring to the length of the string?

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I do not understand what you are trying to say

acoustic star
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i am trying to express the 8 i wrote

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let me try to do better

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(*uint16)(unsafe.Add(unsafe.Pointer(&myname)), 8)

we got the pointer here of the string so now we have the location of the pointer in memory

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but 8 means the length the pointer

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if we have

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hello world

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8 refers to the first element of the string

sweet iris
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no

acoustic star
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which is h

sweet iris
#

you are assuming the size of a pointer is 8, which is a problematic assumption as the size of a pointer is architecture dependant

acoustic star
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but

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i get different results to what u are saying

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let me please write some codes and the results

sweet iris
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I have not given you any results

acoustic star
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no no

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u misunderstood

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my results that is what i meant

sweet iris
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I'm just stating that:
1 - the code is just wrong
2 - you are assuming 64 bit pointers

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number 2 is just a note

acoustic star
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let me show

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you

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see

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i told you

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if i do chinese characters

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that would not work

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if i do 16 that would work

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because chinese take more than 1 byte

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and 8 is a byte

sweet iris
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the code is still both illegal and incorrect

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this has nothing to do with the string data

acoustic star
#

why is it illegal and not correct explain more please

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is it a ub ?

sweet iris
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it is illegal because strings are immutable

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it is incorrect because it will only work on little endian machines

acoustic star
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how immutable i don't understand ?

sweet iris
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100% immutable

acoustic star
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is there anything i can do to check ?

sweet iris
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check what?

acoustic star
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if it is immutable

sweet iris
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read the spec

acoustic star
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it seems mutable to me

sweet iris
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with unsafe everything is mutable

acoustic star
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but anyways i will check what you said

sweet iris
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I'm not talking about variables of type string

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I'm talking about strings

sweet iris
acoustic star
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of course they are immutable

sweet iris
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ok so stop trying to mutate them

acoustic star
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??!!

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i still don't understand you

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if i mutate them i will get unknown stuff for sure

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which mutate are you talking about ?

sweet iris
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not sure there is more than one definition 🙂

acoustic star
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very strange mutating a constant value

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?!!!!!

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what

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crazy

sweet iris
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what are you trying to do

acoustic star
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i am trying to understand what you said

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it is very strange

sweet iris
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what are you trying to do with the code

acoustic star
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just practice

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and making sure of the information

sweet iris
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what are you trying to accomplish with the code

acoustic star
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to be honest

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i want to do slicing

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using pointers

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like

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string

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and stringdata

sweet iris
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sliced := str[3:42]

acoustic star
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but differently

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no

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using pointers

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i know that

sweet iris
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there you go

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stop using unsafe, learn the language first

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then you can do whatever you want

acoustic star
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what about

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pointer arithmetic

sweet iris
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go doesn't have pointer arithmetic

acoustic star
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it does

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unsafe

sweet iris
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unsafe is not go

acoustic star
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???

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what

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what do you mean

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they told me

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unsafe

sweet iris
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who's they

acoustic star
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google

sweet iris
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google told you unsafe?

acoustic star
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damn they wasted my time

acoustic star
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fo uintptr

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and then

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they told me it is for pointers

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and then

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i encountered arithmetic pointers

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and then

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started digging

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and then

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i found unsafe

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see ? it is like a loop

sweet iris
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and then we told you to drop unsafe and learn the language

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and you kept digging

acoustic star
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damn

sweet iris
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stop digging, learn the language

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learning unsafe is not part of learning the language

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and learning the language (among other thigs) is prerequisite knowledge to learn unsafe

acoustic star
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what can i use unsafe for tho ?

sweet iris
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nothing, unsafe is useless, drop it

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learn the language

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then we talk

acoustic star
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ok brother

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you are amazing brother

elfin relic
acoustic star
elfin relic
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the only case you will need uintptr is finalizer, or operate with C library

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but finalizer is also recommend only use with C lib as well

acoustic star
#

i see