[go-nuts] Re: Confused about heap usage for empty slices
(Actually, that address is an address on the stack, but that's only because
the backing store for emptySlice does not escape. It should also take ~no
space.)
On Wednesday, September 7, 2022 at 4:53:12 PM UTC-7 Keith Randall wrote:
> That address is not in the heap. It is the address of a special word in
> the runtime, called runtime.zerobase, which is explicitly for this purpose.
> It is a place to point things that need to be non-nil but have no size.
>
> On Wednesday, September 7, 2022 at 12:01:28 PM UTC-7 me...@pobox.com
> wrote:
>
>> Running this:
>>
>> emptyslice := []string{}
>> sh := (*reflect.SliceHeader)(unsafe.Pointer())
>> fmt.Printf("empty slice cap = %d\n", sh.Cap)
>> fmt.Printf("empty slice len = %d\n", sh.Len)
>> fmt.Printf("empty slice uintptr = %v\n", sh.Data)
>>
>> Output:
>>
>> empty slice cap = 0
>> empty slice len = 0
>> empty slice uintptr = 824634224152
>>
>> The non-zero uintptr suggests that something is allocated on the heap.
>> But the cap is 0, so any backing array should have a size of 0. So what is
>> allocated on the heap? Surely not an array of size 0?
>>
>>
>> mathew
>>
>
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[go-nuts] Re: Confused about heap usage for empty slices
That address is not in the heap. It is the address of a special word in the
runtime, called runtime.zerobase, which is explicitly for this purpose. It
is a place to point things that need to be non-nil but have no size.
On Wednesday, September 7, 2022 at 12:01:28 PM UTC-7 me...@pobox.com wrote:
> Running this:
>
> emptyslice := []string{}
> sh := (*reflect.SliceHeader)(unsafe.Pointer())
> fmt.Printf("empty slice cap = %d\n", sh.Cap)
> fmt.Printf("empty slice len = %d\n", sh.Len)
> fmt.Printf("empty slice uintptr = %v\n", sh.Data)
>
> Output:
>
> empty slice cap = 0
> empty slice len = 0
> empty slice uintptr = 824634224152
>
> The non-zero uintptr suggests that something is allocated on the heap. But
> the cap is 0, so any backing array should have a size of 0. So what is
> allocated on the heap? Surely not an array of size 0?
>
>
> mathew
>
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[go-nuts] Confused about heap usage for empty slices
Running this:
emptyslice := []string{}
sh := (*reflect.SliceHeader)(unsafe.Pointer())
fmt.Printf("empty slice cap = %d\n", sh.Cap)
fmt.Printf("empty slice len = %d\n", sh.Len)
fmt.Printf("empty slice uintptr = %v\n", sh.Data)
Output:
empty slice cap = 0
empty slice len = 0
empty slice uintptr = 824634224152
The non-zero uintptr suggests that something is allocated on the heap. But
the cap is 0, so any backing array should have a size of 0. So what is
allocated on the heap? Surely not an array of size 0?
mathew
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Re: [go-nuts] Assigning struct values
On Wed, Sep 7, 2022 at 12:28 PM Mustafa Durukan
wrote:
>
>
> *fakeObject := tt.Object.(TypeOfStruct)object := Object.(TypeOfStruct)*
If you can include the definitions of tt, explain what you want to do, and
what you mean by "didn't work", someone may be able to answer this
question. Without those, it is not clear what you are trying to achieve.
>
>
> *fakeObject.Field = object.FieldfakeObject.Field2 = object.Field2*
>
> I have case like that.
> I want to assign sme object values to tt.Object but when i try to assign
> it assings to fakeObject i mean copy of tt.Object so I cant assign
>
> I tried these assigns
>
> *tt.Object.(TypeOfStruct).Field =
> object.Fieldtt.Object.(TypeOfStruct).Field2 = object.Field2*
>
> or
>
>
>
> *tt.Object:= tt.Object.(TypeOfStruct)tt.Object.Field =
> object.Fieldtt.Object.Field2 = object.Field2*
>
> But both of them didnt work
> How should i achieve it?
> btw tt.Object and Object are interface{} of course
>
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>
> .
>
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[go-nuts] Assigning struct values
*fakeObject := tt.Object.(TypeOfStruct)object :=
Object.(TypeOfStruct)fakeObject.Field = object.FieldfakeObject.Field2 =
object.Field2*
I have case like that.
I want to assign sme object values to tt.Object but when i try to assign it
assings to fakeObject i mean copy of tt.Object so I cant assign
I tried these assigns
*tt.Object.(TypeOfStruct).Field =
object.Fieldtt.Object.(TypeOfStruct).Field2 = object.Field2*
or
*tt.Object:= tt.Object.(TypeOfStruct)tt.Object.Field =
object.Fieldtt.Object.Field2 = object.Field2*
But both of them didnt work
How should i achieve it?
btw tt.Object and Object are interface{} of course
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