world: fix worldgen

internal/util/unsafe.go

@@ -0,0 +1,42 @@
+package util
+
+import (
+	"fmt"
+	"reflect"
+	"unsafe"
+)
+
+// Ptr returns the pointer to these things:
+//   - First element of a slice or array, nil if it has zero length;
+//   - The pointer itself if the parameter is a pointer, pointing to an scalar value.
+// It panics otherwise.
+func Ptr(d interface{}) (addr unsafe.Pointer) {
+	if d == nil {
+		return unsafe.Pointer(nil)
+	}
+
+	v := reflect.ValueOf(d)
+	switch v.Type().Kind() {
+	case reflect.Ptr:
+		e := v.Elem()
+		switch e.Kind() {
+		case
+			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
+			reflect.Float32, reflect.Float64:
+			addr = unsafe.Pointer(e.UnsafeAddr())
+		default:
+			panic(fmt.Errorf("unsupported pointer to type %s; must be a slice or pointer to a singular scalar value or the first element of an array or slice", e.Kind()))
+		}
+
+	case reflect.Slice, reflect.Array:
+		if v.Len() != 0 {
+			addr = unsafe.Pointer(v.Index(0).UnsafeAddr())
+		}
+	case reflect.Uintptr:
+		addr = unsafe.Pointer(d.(uintptr))
+	default:
+		panic(fmt.Errorf("unsupported type %s; must be a slice or pointer to a singular scalar value or the first element of an array or slice", v.Type()))
+	}
+	return
+}