Why Can\'t I Directly Convert Between Slices of Different Types in Go?

Type Conversion Restrictions in Go

Go enforces strict typing rules, which can prevent seemingly obvious conversions between slices of different types containing the same underlying elements. This restriction is evident in the following code:

package main

import "fmt"

type Card string
type Hand []Card

func NewHand(cards []Card) Hand {
    hand := Hand(cards)
    return hand
}

func main() {
    value := []string{"a", "b", "c"}
    firstHand := NewHand(value)
    fmt.Println(firstHand)
}

Despite the similarity between []string and []Card, the compiler reports an error:

cannot use value (type []string) as type []Card in argument to NewHand

Rationale

Go's specification prohibits this conversion to prevent accidental type conversions between unrelated types that coincidentally share the same structure.

Solutions

• Safe Copy: The recommended approach is to copy the contents of the slice to the desired type.
• Unsafe Pointer Conversion (Unsafe): This technique bypasses the type system and allows direct conversion using the unsafe package, but it should be used with caution.

value := []string{"a", "b", "c"}
cards := *(*[]Card)(unsafe.Pointer(&value))
firstHand := NewHand(cards)

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