go - 不能将append(* pairs，Pairliteral)(Pairs)类型用作* Pairs在分配中

Question

我正在编写一个代码来处理warehouse[item[batch, qty]]的组合，然后将基于[batch, qty]的batch与qty的总和分组。我的代码是:

package main

import "fmt"

type Inventory struct {   //instead of: map[string]map[string]Pairs
    Warehouse string
    Item      string
    Batches   Pairs
} 
type Pairs []Pair
type Pair struct {
    Key   string
    Value float64
}

func main() {
    fmt.Println("Hello, 世界")
    var inventory = Inventory{} // or: new(Inventory) noth are working //warehouse[item[batch, qty]]
    inventory.Warehouse = "DMM"
    inventory.Item = "Helmet"
    inventory.Batches = append(inventory.Batches, Pair{"Jan", 10})
    inventory.Batches = append(inventory.Batches, Pair{"Jan", 30})
    inventory.Batches = append(inventory.Batches, Pair{"Feb", 30})
    fmt.Printf("%v\n", inventory)
    inventory.Batches.group()
}

func (p *Pairs) group() {
    sum := make(map[string]float64)
    pairs := new(Pairs)
    for _, el := range *p {
        sum[el.Key] = sum[el.Key] + el.Value
    }
    fmt.Printf("%v %T\n", sum, sum)
    for k, v := range sum {
        pairs = append(*pairs, Pair{k, v})     // <--------------- here is the error
    }
    fmt.Printf("%v %T\n", pairs, pairs)
}

但是我在分组时遇到了提到的错误:

# _/C_/Users/HASAN~1.YOU/AppData/Local/Temp/present-048467841
.\prog.go:36:9: cannot use append(*pairs, Pair literal) (type Pairs) as type *Pairs in assignment

Program exited: exit status 2

Answer 1

意见箱，有2个潜在答案:

将pairs定义为定义var pairs Pairs的Pairs，而不是定义pairs := new(Pairs)的*Pairs

分配两侧的pairs取消引用为:*pairs = append(*pairs, Pair{k, v})

所以现在对我来说完整的工作代码是:

package main

import "fmt"

type Inventory struct { //instead of: map[string]map[string]Pairs
    Warehouse string
    Item      string
    Batches   Pairs
}
type Pairs []Pair
type Pair struct {
    Key   string
    Value float64
}

func main() {
    fmt.Println("Hello, 世界")
    var inventory = Inventory{} // or: new(Inventory) noth are working //warehouse[item[batch, qty]]
    inventory.Warehouse = "DMM"
    inventory.Item = "Helmet"
    inventory.Batches = append(inventory.Batches, Pair{"Jan", 10})
    inventory.Batches = append(inventory.Batches, Pair{"Jan", 30})
    inventory.Batches = append(inventory.Batches, Pair{"Feb", 30})
    fmt.Printf("%v\n", inventory)
    result := inventory.Batches.group()
    fmt.Printf("%v %T\n", result, result)
}

func (p *Pairs) group() Pairs {
    sum := make(map[string]float64)
    pairs := new(Pairs)
    // var pairs Pairs
    for _, el := range *p {
        sum[el.Key] = sum[el.Key] + el.Value
    }
    for k, v := range sum {
        *pairs = append(*pairs, Pair{k, v}) // with pairs := new(Pairs)
        // pairs = append(pairs, Pair{k, v})   // var pairs Pairs
    }
    return *pairs
}

输出为:

Hello, 世界
{DMM Helmet [{Jan 10} {Jan 30} {Feb 30}]}
[{Jan 40} {Feb 30}] main.Pairs

Program exited.