package constant

Import Path
	go/constant (on go.dev)

Dependency Relation
	imports 9 packages, and imported by 4 packages


Involved Source Files

	    kind_string.go
	
		Package constant implements Values representing untyped
		Go constants and their corresponding operations.
		
		A special Unknown value may be used when a value
		is unknown due to an error. Operations on unknown
		values produce unknown values unless specified
		otherwise.


Code Examples

	
		package main
		
		import (
			"fmt"
			"go/constant"
			"go/token"
		)
		
		func main() {
			// 11 / 0.5
			a := constant.MakeUint64(11)
			b := constant.MakeFloat64(0.5)
			c := constant.BinaryOp(a, token.QUO, b)
			fmt.Println(c)
		
		}

	
		package main
		
		import (
			"fmt"
			"go/constant"
			"go/token"
			"sort"
		)
		
		func main() {
			vs := []constant.Value{
				constant.MakeString("Z"),
				constant.MakeString("bacon"),
				constant.MakeString("go"),
				constant.MakeString("Frame"),
				constant.MakeString("defer"),
				constant.MakeFromLiteral(`"a"`, token.STRING, 0),
			}
		
			sort.Slice(vs, func(i, j int) bool {
				// Equivalent to vs[i] <= vs[j].
				return constant.Compare(vs[i], token.LEQ, vs[j])
			})
		
			for _, v := range vs {
				fmt.Println(constant.StringVal(v))
			}
		
		}

	
		package main
		
		import (
			"fmt"
			"go/constant"
			"go/token"
		)
		
		func main() {
			zero := constant.MakeInt64(0)
			one := constant.MakeInt64(1)
			negOne := constant.MakeInt64(-1)
		
			mkComplex := func(a, b constant.Value) constant.Value {
				b = constant.MakeImag(b)
				return constant.BinaryOp(a, token.ADD, b)
			}
		
			vs := []constant.Value{
				negOne,
				mkComplex(zero, negOne),
				mkComplex(one, negOne),
				mkComplex(negOne, one),
				mkComplex(negOne, negOne),
				zero,
				mkComplex(zero, zero),
				one,
				mkComplex(zero, one),
				mkComplex(one, one),
			}
		
			for _, v := range vs {
				fmt.Printf("% d %s\n", constant.Sign(v), v)
			}
		
		}

	
		package main
		
		import (
			"fmt"
			"go/constant"
			"go/token"
		)
		
		func main() {
			vs := []constant.Value{
				constant.MakeBool(true),
				constant.MakeFloat64(2.7),
				constant.MakeUint64(42),
			}
		
			for i, v := range vs {
				switch v.Kind() {
				case constant.Bool:
					vs[i] = constant.UnaryOp(token.NOT, v, 0)
		
				case constant.Float:
					vs[i] = constant.UnaryOp(token.SUB, v, 0)
		
				case constant.Int:
					// Use 16-bit precision.
					// This would be equivalent to ^uint16(v).
					vs[i] = constant.UnaryOp(token.XOR, v, 16)
				}
			}
		
			for _, v := range vs {
				fmt.Println(v)
			}
		
		}

	
		package main
		
		import (
			"fmt"
			"go/constant"
			"math"
		)
		
		func main() {
			maxint := constant.MakeInt64(math.MaxInt64)
			fmt.Printf("%v\n", constant.Val(maxint))
		
			e := constant.MakeFloat64(math.E)
			fmt.Printf("%v\n", constant.Val(e))
		
			b := constant.MakeBool(true)
			fmt.Printf("%v\n", constant.Val(b))
		
			b = constant.Make(false)
			fmt.Printf("%v\n", constant.Val(b))
		
		}

	
		package main
		
		import (
			"fmt"
			"go/constant"
			"go/token"
		)
		
		func main() {
			// Create the complex number 2.3 + 5i.
			ar := constant.MakeFloat64(2.3)
			ai := constant.MakeImag(constant.MakeInt64(5))
			a := constant.BinaryOp(ar, token.ADD, ai)
		
			// Compute (2.3 + 5i) * 11.
			b := constant.MakeUint64(11)
			c := constant.BinaryOp(a, token.MUL, b)
		
			// Convert c into a complex128.
			Ar, exact := constant.Float64Val(constant.Real(c))
			if !exact {
				fmt.Printf("Could not represent real part %s exactly as float64\n", constant.Real(c))
			}
			Ai, exact := constant.Float64Val(constant.Imag(c))
			if !exact {
				fmt.Printf("Could not represent imaginary part %s as exactly as float64\n", constant.Imag(c))
			}
			C := complex(Ar, Ai)
		
			fmt.Println("literal", 25.3+55i)
			fmt.Println("go/constant", c)
			fmt.Println("complex128", C)
		
		}




Package-Level Type Names (total 2)


	/* sort by:  |  */
	
		Kind specifies the kind of value represented by a [Value].

		
			( Kind) String() string
		
			 Kind : expvar.Var
			 Kind : fmt.Stringer
		
			func Value.Kind() Kind
		
			const Bool
			const Complex
			const Float
			const Int
			const String
			const Unknown


	
		A Value represents the value of a Go constant.

		
			
				ExactString returns an exact, quoted (human-readable) form of the value.
				If the Value is of Kind String, use StringVal to obtain the unquoted string.

			
				Kind returns the value kind.

			
				String returns a short, quoted (human-readable) form of the value.
				For numeric values, the result may be an approximation;
				for String values the result may be a shortened string.
				Use ExactString for a string representing a value exactly.

		
			 Value : expvar.Var
			 Value : fmt.Stringer
		
			func BinaryOp(x_ Value, op token.Token, y_ Value) Value
			func Denom(x Value) Value
			func Imag(x Value) Value
			func Make(x any) Value
			func MakeBool(b bool) Value
			func MakeFloat64(x float64) Value
			func MakeFromBytes(bytes []byte) Value
			func MakeFromLiteral(lit string, tok token.Token, zero uint) Value
			func MakeImag(x Value) Value
			func MakeInt64(x int64) Value
			func MakeString(s string) Value
			func MakeUint64(x uint64) Value
			func MakeUnknown() Value
			func Num(x Value) Value
			func Real(x Value) Value
			func Shift(x Value, op token.Token, s uint) Value
			func ToComplex(x Value) Value
			func ToFloat(x Value) Value
			func ToInt(x Value) Value
			func UnaryOp(op token.Token, y Value, prec uint) Value
			func go/types.(*Const).Val() Value
			func internal/pkgbits.(*Decoder).Value() Value
		
			func BinaryOp(x_ Value, op token.Token, y_ Value) Value
			func BinaryOp(x_ Value, op token.Token, y_ Value) Value
			func BitLen(x Value) int
			func BoolVal(x Value) bool
			func Bytes(x Value) []byte
			func Compare(x_ Value, op token.Token, y_ Value) bool
			func Compare(x_ Value, op token.Token, y_ Value) bool
			func Denom(x Value) Value
			func Float32Val(x Value) (float32, bool)
			func Float64Val(x Value) (float64, bool)
			func Imag(x Value) Value
			func Int64Val(x Value) (int64, bool)
			func MakeImag(x Value) Value
			func Num(x Value) Value
			func Real(x Value) Value
			func Shift(x Value, op token.Token, s uint) Value
			func Sign(x Value) int
			func StringVal(x Value) string
			func ToComplex(x Value) Value
			func ToFloat(x Value) Value
			func ToInt(x Value) Value
			func Uint64Val(x Value) (uint64, bool)
			func UnaryOp(op token.Token, y Value, prec uint) Value
			func Val(x Value) any
			func go/types.NewConst(pos token.Pos, pkg *types.Package, name string, typ types.Type, val Value) *types.Const
			func internal/pkgbits.(*Encoder).Value(val Value)




Package-Level Functions (total 31)


	
		BinaryOp returns the result of the binary expression x op y.
		The operation must be defined for the operands. If one of the
		operands is [Unknown], the result is [Unknown].
		BinaryOp doesn't handle comparisons or shifts; use [Compare]
		or [Shift] instead.
		
		To force integer division of [Int] operands, use op == [token.QUO_ASSIGN]
		instead of [token.QUO]; the result is guaranteed to be [Int] in this case.
		Division by zero leads to a run-time panic.


	
		BitLen returns the number of bits required to represent
		the absolute value x in binary representation; x must be an [Int] or an [Unknown].
		If x is [Unknown], the result is 0.


	
		BoolVal returns the Go boolean value of x, which must be a [Bool] or an [Unknown].
		If x is [Unknown], the result is false.


	
		Bytes returns the bytes for the absolute value of x in little-
		endian binary representation; x must be an [Int].


	
		Compare returns the result of the comparison x op y.
		The comparison must be defined for the operands.
		If one of the operands is [Unknown], the result is
		false.


	
		Denom returns the denominator of x; x must be [Int], [Float], or [Unknown].
		If x is [Unknown], or if it is too large or small to represent as a
		fraction, the result is [Unknown]. Otherwise the result is an [Int] >= 1.


	
		Float32Val is like [Float64Val] but for float32 instead of float64.


	
		Float64Val returns the nearest Go float64 value of x and whether the result is exact;
		x must be numeric or an [Unknown], but not [Complex]. For values too small (too close to 0)
		to represent as float64, [Float64Val] silently underflows to 0. The result sign always
		matches the sign of x, even for 0.
		If x is [Unknown], the result is (0, false).


	
		Imag returns the imaginary part of x, which must be a numeric or unknown value.
		If x is [Unknown], the result is [Unknown].


	
		Int64Val returns the Go int64 value of x and whether the result is exact;
		x must be an [Int] or an [Unknown]. If the result is not exact, its value is undefined.
		If x is [Unknown], the result is (0, false).


	
		Make returns the [Value] for x.
		
			type of x        result Kind
			----------------------------
			bool             Bool
			string           String
			int64            Int
			*big.Int         Int
			*big.Float       Float
			*big.Rat         Float
			anything else    Unknown


	
		MakeBool returns the [Bool] value for b.


	
		MakeFloat64 returns the [Float] value for x.
		If x is -0.0, the result is 0.0.
		If x is not finite, the result is an [Unknown].


	
		MakeFromBytes returns the [Int] value given the bytes of its little-endian
		binary representation. An empty byte slice argument represents 0.


	
		MakeFromLiteral returns the corresponding integer, floating-point,
		imaginary, character, or string value for a Go literal string. The
		tok value must be one of [token.INT], [token.FLOAT], [token.IMAG],
		[token.CHAR], or [token.STRING]. The final argument must be zero.
		If the literal string syntax is invalid, the result is an [Unknown].


	
		MakeImag returns the [Complex] value x*i;
		x must be [Int], [Float], or [Unknown].
		If x is [Unknown], the result is [Unknown].


	
		MakeInt64 returns the [Int] value for x.


	
		MakeString returns the [String] value for s.


	
		MakeUint64 returns the [Int] value for x.


	
		MakeUnknown returns the [Unknown] value.


	
		Num returns the numerator of x; x must be [Int], [Float], or [Unknown].
		If x is [Unknown], or if it is too large or small to represent as a
		fraction, the result is [Unknown]. Otherwise the result is an [Int]
		with the same sign as x.


	
		Real returns the real part of x, which must be a numeric or unknown value.
		If x is [Unknown], the result is [Unknown].


	
		Shift returns the result of the shift expression x op s
		with op == [token.SHL] or [token.SHR] (<< or >>). x must be
		an [Int] or an [Unknown]. If x is [Unknown], the result is x.


	
		Sign returns -1, 0, or 1 depending on whether x < 0, x == 0, or x > 0;
		x must be numeric or [Unknown]. For complex values x, the sign is 0 if x == 0,
		otherwise it is != 0. If x is [Unknown], the result is 1.


	
		StringVal returns the Go string value of x, which must be a [String] or an [Unknown].
		If x is [Unknown], the result is "".


	
		ToComplex converts x to a [Complex] value if x is representable as a [Complex].
		Otherwise it returns an [Unknown].


	
		ToFloat converts x to a [Float] value if x is representable as a [Float].
		Otherwise it returns an [Unknown].


	
		ToInt converts x to an [Int] value if x is representable as an [Int].
		Otherwise it returns an [Unknown].


	
		Uint64Val returns the Go uint64 value of x and whether the result is exact;
		x must be an [Int] or an [Unknown]. If the result is not exact, its value is undefined.
		If x is [Unknown], the result is (0, false).


	
		UnaryOp returns the result of the unary expression op y.
		The operation must be defined for the operand.
		If prec > 0 it specifies the ^ (xor) result size in bits.
		If y is [Unknown], the result is [Unknown].


	
		Val returns the underlying value for a given constant. Since it returns an
		interface, it is up to the caller to type assert the result to the expected
		type. The possible dynamic return types are:
		
			x Kind             type of result
			-----------------------------------------
			Bool               bool
			String             string
			Int                int64 or *big.Int
			Float              *big.Float or *big.Rat
			everything else    nil




Package-Level Constants (total 6)


	
		non-numeric values


	const Complex Kind = 5
	const Float Kind = 4
	
		numeric values


	const String Kind = 2
	
		unknown values