(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(&emptyslice))
>> 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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