go issue50690a 源码
golang issue50690a 代码
文件路径：/test/typeparam/issue50690a.go
// run
// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"fmt"
)
// Numeric expresses a type constraint satisfied by any numeric type.
type Numeric interface {
~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 |
~int | ~int8 | ~int16 | ~int32 | ~int64 |
~float32 | ~float64 |
~complex64 | ~complex128
}
// Sum returns the sum of the provided arguments.
func Sum[T Numeric](args ...T) T {
var sum T
for i := 0; i < len(args); i++ {
sum += args[i]
}
return sum
}
// Ledger is an identifiable, financial record.
type Ledger[T ~string, K Numeric] struct {
// ID identifies the ledger.
ID_ T
// Amounts is a list of monies associated with this ledger.
Amounts_ []K
// SumFn is a function that can be used to sum the amounts
// in this ledger.
SumFn_ func(...K) K
}
// Field accesses through type parameters are disabled
// until we have a more thorough understanding of the
// implications on the spec. See issue #51576.
// Use accessor methods instead.
func (l Ledger[T, _]) ID() T { return l.ID_ }
func (l Ledger[_, K]) Amounts() []K { return l.Amounts_ }
func (l Ledger[_, K]) SumFn() func(...K) K { return l.SumFn_ }
func PrintLedger[
T ~string,
K Numeric,
L interface {
~struct {
ID_ T
Amounts_ []K
SumFn_ func(...K) K
}
ID() T
Amounts() []K
SumFn() func(...K) K
},
](l L) {
fmt.Printf("%s has a sum of %v\n", l.ID(), l.SumFn()(l.Amounts()...))
}
func main() {
PrintLedger(Ledger[string, int]{
ID_: "fake",
Amounts_: []int{1, 2, 3},
SumFn_: Sum[int],
})
}
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