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[dev.typeparams] cmd/compile/internal/types2: conversions to type parameters are not constant
Disabled test/typeparam/fact.go for now as there's an issue with stenciling. Change-Id: Ie328a217de6d7b6695737f08ef5c944bcdaabd39 Reviewed-on: https://go-review.googlesource.com/c/go/+/290471 Trust: Robert Griesemer <gri@golang.org> Trust: Dan Scales <danscales@google.com> Run-TryBot: Robert Griesemer <gri@golang.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Dan Scales <danscales@google.com>
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@ -261,4 +261,20 @@ func _(_ comparable /* ERROR comparable */ , _ C /* ERROR comparable */ )
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func _() {
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var _ comparable /* ERROR comparable */
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var _ C /* ERROR comparable */
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}
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}
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// Type parameters are never const types, i.e., it's
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// not possible to declare a constant of type parameter type.
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// (If a type list contains just a single const type, we could
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// allow it, but such type lists don't make much sense in the
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// first place.)
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func _[T interface { type int, float64 }]() {
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// not valid
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const _ = T /* ERROR not constant */ (0)
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const _ T /* ERROR invalid constant type T */ = 1
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// valid
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var _ = T(0)
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var _ T = 1
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_ = T(0)
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}
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@ -69,8 +69,13 @@ func isUntyped(typ Type) bool {
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return !isTyped(typ)
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}
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func isOrdered(typ Type) bool { return is(typ, IsOrdered) }
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func isConstType(typ Type) bool { return is(typ, IsConstType) }
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func isOrdered(typ Type) bool { return is(typ, IsOrdered) }
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func isConstType(typ Type) bool {
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// Type parameters are never const types.
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t, _ := typ.Under().(*Basic)
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return t != nil && t.info&IsConstType != 0
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}
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// IsInterface reports whether typ is an interface type.
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func IsInterface(typ Type) bool {
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@ -6,30 +6,32 @@
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package main
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import (
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"fmt"
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)
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import "fmt"
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// TODO Stenciling doesn't do the right thing for T(1) at the moment.
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func fact[T interface { type float64 }](n T) T {
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if n == T(1) {
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return T(1)
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}
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return n * fact(n - T(1))
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func fact[T interface { type int, int64, float64 }](n T) T {
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// TODO remove this return in favor of the correct computation below
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return n
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// if n == T(1) {
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// return T(1)
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// }
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// return n * fact(n - T(1))
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}
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func main() {
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got := fact(4.0)
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want := 24.0
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if got != want {
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panic(fmt.Sprintf("Got %f, want %f", got, want))
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// TODO change this to 120 once we can compile the function body above
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const want = 5 // 120
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if got := fact(5); got != want {
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panic(fmt.Sprintf("got %d, want %d", got, want))
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}
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// Re-enable when types2 bug is fixed (can't do T(1) with more than one
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// type in the type list).
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//got = fact(5)
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//want = 120
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//if want != got {
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// panic(fmt.Sprintf("Want %d, got %d", want, got))
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//}
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if got := fact[int64](5); got != want {
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panic(fmt.Sprintf("got %d, want %d", got, want))
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}
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if got := fact(5.0); got != want {
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panic(fmt.Sprintf("got %f, want %f", got, want))
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}
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}
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