Maximum length of a slice in Go

Question

I have the following code running in a 64-bit linux OS in a 4Gb machine:

package main

import (
    \"fmt\"
    \"math\"
)

func main() {
    r := make([]boo         


        

Answer 1

According to the docs, The elements can be addressed by integer indices 0 through len(s)-1. This means the maximum capacity for a slice is the size of the default integer on the target build.

EDIT: From looking at the source code, it appears that there is a safety check to make sure this size of slice is at all possible:

func makeslice(t *slicetype, len64 int64, cap64 int64) sliceStruct {
    // NOTE: The len > MaxMem/elemsize check here is not strictly necessary,
    // but it produces a 'len out of range' error instead of a 'cap out of range' error
    // when someone does make([]T, bignumber). 'cap out of range' is true too,
    // but since the cap is only being supplied implicitly, saying len is clearer.
    // See issue 4085.
    len := int(len64)
    if len64 < 0 || int64(len) != len64 || t.elem.size > 0 && uintptr(len) > maxmem/uintptr(t.elem.size) {
        panic(errorString("makeslice: len out of range"))
    }

So in this case, it looks like uintptr(len) > maxmem/uintptr(t.elem.size) so we're not allowed to do this size of an allocation.

However when I allocate struct{} which takes no memory, this size is allowed:

func main(){
    r := make([]struct{}, math.MaxInt64)
    fmt.Println(len(r))
}
// prints 9223372036854775807