CODEWITHSUNDEEP
goslice
Hai . Z
Hai . Z

Reputation: 121

which type's size is zero in slice of golang?

which type's size is zero in slice of golang?

When I read the source code of golang slice, I found a code et.size == 0. so I want to know which type's size is 0?

func growslice(et *_type, old slice, cap int) slice {
    ...
    if et.size == 0 {
        if cap < old.cap {
            panic(errorString("growslice: cap out of range"))
        }

        return slice{unsafe.Pointer(&zerobase), old.len, cap}
    }
    ...
}

Upvotes: 1

Views: 838

Answers (1)

peterSO
peterSO

Reputation: 166569

The Go Programming Language Specification

Size and alignment guarantees

A struct or array type has size zero if it contains no fields (or elements, respectively) that have a size greater than zero. Two distinct zero-size variables may have the same address in memory.

For example,

package main

import (
    "fmt"
    "unsafe"
)

func main() {
    type zero struct{}
    fmt.Println(unsafe.Sizeof(zero{}))
    slice := make([]zero, 7)
    fmt.Printf("%d %v %p %p\n", len(slice), slice, &slice[0], &slice[len(slice)-1])
}

Playground: https://play.golang.org/p/pn8Rz0IorwD

Output:

0
7 [{} {} {} {} {} {} {}] 0x1c4c84 0x1c4c84

Upvotes: 2

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