[runtime] gostring question

[Bill Morgan]

I'm a C programmer so maybe this is a dumb question but, why does this code in runtime/gostring.go allocate (rawstring) then copy data (memmove) instead of just making the stringStruct.str point at the incoming data? i.e. copy the pointer instead of allocating+copying data.

func gostring(p *byte) string {

l := findnull(p)

if l == 0 {

return ""

}

s, b := rawstring(l)

memmove(unsafe.Pointer(&b[0]), unsafe.Pointer(p), uintptr(l))

return s

}

[Bill Morgan]

looks like the code came from commit: 61dca94e107170d2ff3beb13bb9fa5ce49d8d6fd and the old string.c file had a gostringnocopy that copied the ptr instead of allocating and copying. 

Wondering why that was removed. I guess there must be some reason that you must have a duplicate copy.

 

[Kurtis Rader]

On Tue, Jun 23, 2020 at 5:32 PM Bill Morgan <arthurwil...@gmail.com> wrote:

I'm a C programmer so maybe this is a dumb question but, why does this code in runtime/gostring.go allocate (rawstring) then copy data (memmove) instead of just making the stringStruct.str point at the incoming data? i.e. copy the pointer instead of allocating+copying data.

Go strings are immutable: https://golang.org/ref/spec#String_types.

--

Kurtis Rader

Caretaker of the exceptional canines Junior and Hank

[keith....@gmail.com]

Yes, we can't depend on the data at *p to remain constant. We need to snapshot it at the moment of the gostring call.