Remove notion of core types

// This program demonstrates the current limitation that a slice expression
// cannot be applied directly to a type parameter. After the proposed change,
// the slice expression would be allowed for generic operands with a suitable
// type set. Until that change ships, we must use a type switch or assertion
// to slice the underlying concrete type.

package main

import (
	"fmt"
)

// Constraint allows either a slice of int or a string.
type Constraint interface {
	~[]int | ~string
}

// sliceGeneric attempts to slice a value of type T.
// Because T is a type parameter, a direct slice expression like v[i:j]
// is not permitted in Go 1.27.1. We work around this by using a type switch.
func sliceGeneric[T Constraint](v T, i, j int) interface{} {
	switch x := any(v).(type) {
	case []int:
		return x[i:j]
	case string:
		return x[i:j]
	default:
		return nil
	}
}

func main() {
	// Example with a slice of int.
	intSlice := []int{10, 20, 30, 40, 50}
	fmt.Println("Slicing []int:", sliceGeneric(intSlice, 1, 4))

	// Example with a string.
	str := "hello world"
	fmt.Println("Slicing string:", sliceGeneric(str, 6, 11))
}