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|
package vals
import (
"math"
"math/big"
"unsafe"
)
// Ordering relationship between two Elvish values.
type Ordering uint8
// Possible Ordering values.
const (
CmpLess Ordering = iota
CmpEqual
CmpMore
CmpUncomparable
)
// Cmp compares two Elvish values and returns the ordering relationship between
// them. Cmp(a, b) returns CmpEqual iff Equal(a, b) is true or both a and b are
// NaNs.
func Cmp(a, b any) Ordering {
return cmpInner(a, b, Cmp)
}
func cmpInner(a, b any, recurse func(a, b any) Ordering) Ordering {
// Keep the branches in the same order as [Equal].
switch a := a.(type) {
case nil:
if b == nil {
return CmpEqual
}
case bool:
if b, ok := b.(bool); ok {
switch {
case a == b:
return CmpEqual
//lint:ignore S1002 using booleans as values, not conditions
case a == false: // b == true is implicit
return CmpLess
default: // a == true && b == false
return CmpMore
}
}
case int, *big.Int, *big.Rat, float64:
switch b.(type) {
case int, *big.Int, *big.Rat, float64:
a, b := UnifyNums2(a, b, 0)
switch a := a.(type) {
case int:
return compareBuiltin(a, b.(int))
case *big.Int:
return compareBuiltin(a.Cmp(b.(*big.Int)), 0)
case *big.Rat:
return compareBuiltin(a.Cmp(b.(*big.Rat)), 0)
case float64:
return compareFloat(a, b.(float64))
default:
panic("unreachable")
}
}
case string:
if b, ok := b.(string); ok {
return compareBuiltin(a, b)
}
case List:
if b, ok := b.(List); ok {
aIt := a.Iterator()
bIt := b.Iterator()
for aIt.HasElem() && bIt.HasElem() {
o := recurse(aIt.Elem(), bIt.Elem())
if o != CmpEqual {
return o
}
aIt.Next()
bIt.Next()
}
switch {
case a.Len() == b.Len():
return CmpEqual
case a.Len() < b.Len():
return CmpLess
default: // a.Len() > b.Len()
return CmpMore
}
}
default:
if Equal(a, b) {
return CmpEqual
}
}
return CmpUncomparable
}
func compareBuiltin[T interface{ int | uintptr | string }](a, b T) Ordering {
if a < b {
return CmpLess
} else if a > b {
return CmpMore
}
return CmpEqual
}
func compareFloat(a, b float64) Ordering {
// For the sake of ordering, NaN's are considered equal to each
// other and smaller than all numbers
switch {
case math.IsNaN(a):
if math.IsNaN(b) {
return CmpEqual
}
return CmpLess
case math.IsNaN(b):
return CmpMore
case a < b:
return CmpLess
case a > b:
return CmpMore
default: // a == b
return CmpEqual
}
}
// CmpTotal is similar to [Cmp], but uses an artificial total ordering to avoid
// returning [CmpUncomparable]:
//
// - If a and b have different types, it compares their types instead. The
// ordering of types is guaranteed to be consistent during one Elvish
// session, but is otherwise undefined.
//
// - If a and b have the same type but are considered uncomparable by [Cmp],
// it returns [CmpEqual] instead of [CmpUncomparable].
//
// All the underlying Go types of Elvish's number type are considered the same
// type.
//
// This function is mainly useful for sorting Elvish values that are not
// considered comparable by [Cmp]. Using this function as a comparator groups
// values by their types and sorts types that are comparable.
func CmpTotal(a, b any) Ordering {
if o := compareBuiltin(typeOf(a), typeOf(b)); o != CmpEqual {
return o
}
if o := cmpInner(a, b, CmpTotal); o != CmpUncomparable {
return o
}
return CmpEqual
}
var typeOfInt, typeOfMap uintptr
func typeOf(x any) uintptr {
switch x.(type) {
case *big.Int, *big.Rat, float64:
return typeOfInt
case StructMap:
return typeOfMap
}
// The first word of an empty interface is a pointer to the type descriptor.
return *(*uintptr)(unsafe.Pointer(&x))
}
func init() {
typeOfInt = typeOf(0)
typeOfMap = typeOf(EmptyMap)
}
|
