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package structr
import (
"fmt"
"reflect"
"unicode"
"unicode/utf8"
"unsafe"
"github.com/modern-go/reflect2"
"github.com/zeebo/xxh3"
)
type structfield struct {
// _type is the runtime type pointer
// underlying the struct field type.
// used for repacking our own erfaces.
_type reflect2.Type
// offset is the offset in memory
// of this struct field from the
// outer-most value ptr location.
offset uintptr
// hasher is the relevant function
// for hashing value of structfield
// into the supplied hashbuf, where
// return value indicates if zero.
hasher func(*xxh3.Hasher, any) bool
}
// find_field will search for a struct field with given set of names,
// where names is a len > 0 slice of names account for struct nesting.
func find_field(t reflect.Type, names []string) (sfield structfield) {
var (
// is_exported returns whether name is exported
// from a package; can be func or struct field.
is_exported = func(name string) bool {
r, _ := utf8.DecodeRuneInString(name)
return unicode.IsUpper(r)
}
// pop_name pops the next name from
// the provided slice of field names.
pop_name = func() string {
name := names[0]
names = names[1:]
if !is_exported(name) {
panicf("field is not exported: %s", name)
}
return name
}
// field is the iteratively searched
// struct field value in below loop.
field reflect.StructField
)
switch {
// The only 2 types we support are
// structs, and ptrs to a struct.
case t.Kind() == reflect.Struct:
case t.Kind() == reflect.Pointer &&
t.Elem().Kind() == reflect.Struct:
t = t.Elem()
default:
panic("index only support struct{} and *struct{}")
}
for len(names) > 0 {
var ok bool
// Pop next name.
name := pop_name()
// Check for valid struct type.
if t.Kind() != reflect.Struct {
panicf("field %s is not struct: %s", t, name)
}
// Look for next field by name.
field, ok = t.FieldByName(name)
if !ok {
panicf("unknown field: %s", name)
}
// Increment total field offset.
sfield.offset += field.Offset
// Set the next type.
t = field.Type
}
// Get field type as reflect2.
sfield._type = reflect2.Type2(t)
// Find hasher for type.
sfield.hasher = hasher(t)
return
}
// extract_fields extracts given structfields from the provided value type,
// this is done using predetermined struct field memory offset locations.
func extract_fields[T any](value T, fields []structfield) []any {
// Get ptr to raw value data.
ptr := unsafe.Pointer(&value)
// If this is a pointer type deref the value ptr.
if reflect.TypeOf(value).Kind() == reflect.Pointer {
ptr = *(*unsafe.Pointer)(ptr)
}
// Prepare slice of field ifaces.
ifaces := make([]any, len(fields))
for i := 0; i < len(fields); i++ {
// Manually access field at memory offset and pack eface.
ptr := unsafe.Pointer(uintptr(ptr) + fields[i].offset)
ifaces[i] = fields[i]._type.UnsafeIndirect(ptr)
}
return ifaces
}
// data_ptr returns the runtime data ptr associated with value.
func data_ptr(a any) unsafe.Pointer {
return (*struct{ t, v unsafe.Pointer })(unsafe.Pointer(&a)).v
}
// panicf provides a panic with string formatting.
func panicf(format string, args ...any) {
panic(fmt.Sprintf(format, args...))
}
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