// Conversion type-checks the conversion T(x).
// The result is in x.
func (check *Checker) conversion(x *operand, T Type) {
constArg := x.mode == constant
var ok bool
switch {
case constArg && isConstType(T):
// constant conversion
switch t := T.Underlying().(*Basic); {
case representableConst(x.val, check.conf, t.kind, &x.val):
ok = true
case isInteger(x.typ) && isString(t):
codepoint := int64(-1)
if i, ok := exact.Int64Val(x.val); ok {
codepoint = i
}
// If codepoint < 0 the absolute value is too large (or unknown) for
// conversion. This is the same as converting any other out-of-range
// value - let string(codepoint) do the work.
x.val = exact.MakeString(string(codepoint))
ok = true
}
case x.convertibleTo(check.conf, T):
// non-constant conversion
x.mode = value
ok = true
}
if !ok {
check.errorf(x.pos(), "cannot convert %s to %s", x, T)
x.mode = invalid
return
}
// The conversion argument types are final. For untyped values the
// conversion provides the type, per the spec: "A constant may be
// given a type explicitly by a constant declaration or conversion,...".
final := x.typ
if isUntyped(x.typ) {
final = T
// - For conversions to interfaces, use the argument's default type.
// - For conversions of untyped constants to non-constant types, also
// use the default type (e.g., []byte("foo") should report string
// not []byte as type for the constant "foo").
// - Keep untyped nil for untyped nil arguments.
if IsInterface(T) || constArg && !isConstType(T) {
final = defaultType(x.typ)
}
check.updateExprType(x.expr, final, true)
}
x.typ = T
}
// Int64 returns the numeric value of this constant truncated to fit
// a signed 64-bit integer.
//
func (c *Const) Int64() int64 {
switch x := c.Value; x.Kind() {
case exact.Int:
if i, ok := exact.Int64Val(x); ok {
return i
}
return 0
case exact.Float:
f, _ := exact.Float64Val(x)
return int64(f)
}
panic(fmt.Sprintf("unexpected constant value: %T", c.Value))
}
func (check *Checker) arrayLength(e ast.Expr) int64 {
var x operand
check.expr(&x, e)
if x.mode != constant {
if x.mode != invalid {
check.errorf(x.pos(), "array length %s must be constant", &x)
}
return 0
}
if !x.isInteger() {
check.errorf(x.pos(), "array length %s must be integer", &x)
return 0
}
n, ok := exact.Int64Val(x.val)
if !ok || n < 0 {
check.errorf(x.pos(), "invalid array length %s", &x)
return 0
}
return n
}
// index checks an index expression for validity.
// If max >= 0, it is the upper bound for index.
// If index is valid and the result i >= 0, then i is the constant value of index.
func (check *Checker) index(index ast.Expr, max int64) (i int64, valid bool) {
var x operand
check.expr(&x, index)
if x.mode == invalid {
return
}
// an untyped constant must be representable as Int
check.convertUntyped(&x, Typ[Int])
if x.mode == invalid {
return
}
// the index must be of integer type
if !isInteger(x.typ) {
check.invalidArg(x.pos(), "index %s must be integer", &x)
return
}
// a constant index i must be in bounds
if x.mode == constant {
if exact.Sign(x.val) < 0 {
check.invalidArg(x.pos(), "index %s must not be negative", &x)
return
}
i, valid = exact.Int64Val(x.val)
if !valid || max >= 0 && i >= max {
check.errorf(x.pos(), "index %s is out of bounds", &x)
return i, false
}
// 0 <= i [ && i < max ]
return i, true
}
return -1, true
}
// representableConst reports whether x can be represented as
// value of the given basic type kind and for the configuration
// provided (only needed for int/uint sizes).
//
// If rounded != nil, *rounded is set to the rounded value of x for
// representable floating-point values; it is left alone otherwise.
// It is ok to provide the addressof the first argument for rounded.
func representableConst(x exact.Value, conf *Config, as BasicKind, rounded *exact.Value) bool {
switch x.Kind() {
case exact.Unknown:
return true
case exact.Bool:
return as == Bool || as == UntypedBool
case exact.Int:
if x, ok := exact.Int64Val(x); ok {
switch as {
case Int:
var s = uint(conf.sizeof(Typ[as])) * 8
return int64(-1)<<(s-1) <= x && x <= int64(1)<<(s-1)-1
case Int8:
const s = 8
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
case Int16:
const s = 16
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
case Int32:
const s = 32
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
case Int64:
return true
case Uint, Uintptr:
if s := uint(conf.sizeof(Typ[as])) * 8; s < 64 {
return 0 <= x && x <= int64(1)<<s-1
}
return 0 <= x
case Uint8:
const s = 8
return 0 <= x && x <= 1<<s-1
case Uint16:
const s = 16
return 0 <= x && x <= 1<<s-1
case Uint32:
const s = 32
return 0 <= x && x <= 1<<s-1
case Uint64:
return 0 <= x
case Float32, Float64, Complex64, Complex128,
UntypedInt, UntypedFloat, UntypedComplex:
return true
}
}
n := exact.BitLen(x)
switch as {
case Uint, Uintptr:
var s = uint(conf.sizeof(Typ[as])) * 8
return exact.Sign(x) >= 0 && n <= int(s)
case Uint64:
return exact.Sign(x) >= 0 && n <= 64
case Float32, Complex64:
if rounded == nil {
return fitsFloat32(x)
}
r := roundFloat32(x)
if r != nil {
*rounded = r
return true
}
case Float64, Complex128:
if rounded == nil {
return fitsFloat64(x)
}
r := roundFloat64(x)
if r != nil {
*rounded = r
return true
}
case UntypedInt, UntypedFloat, UntypedComplex:
return true
}
case exact.Float:
switch as {
case Float32, Complex64:
if rounded == nil {
return fitsFloat32(x)
}
r := roundFloat32(x)
if r != nil {
*rounded = r
return true
}
case Float64, Complex128:
if rounded == nil {
return fitsFloat64(x)
}
r := roundFloat64(x)
if r != nil {
*rounded = r
return true
}
case UntypedFloat, UntypedComplex:
return true
}
case exact.Complex:
switch as {
case Complex64:
if rounded == nil {
return fitsFloat32(exact.Real(x)) && fitsFloat32(exact.Imag(x))
}
re := roundFloat32(exact.Real(x))
im := roundFloat32(exact.Imag(x))
if re != nil && im != nil {
*rounded = exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
return true
}
case Complex128:
if rounded == nil {
return fitsFloat64(exact.Real(x)) && fitsFloat64(exact.Imag(x))
}
re := roundFloat64(exact.Real(x))
im := roundFloat64(exact.Imag(x))
if re != nil && im != nil {
*rounded = exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
return true
}
case UntypedComplex:
return true
}
case exact.String:
return as == String || as == UntypedString
default:
unreachable()
}
return false
}