我有一个小例子，我尝试在一个函数中填充一个 []Entry(其中 Entry 是一个接口(interface)) slice ，当参数是单个 Entry 时这工作正常，但是当我试图传递一个条目 slice 时我无法通过指针找到我的方式。

package temp

import (
    "encoding/json"

    uuid "github.com/satori/go.uuid"
)

type BaseEntry struct {
    ID uuid.UUID
}

func (entry *BaseEntry) GetID() uuid.UUID {
    return entry.ID
}

type Entry interface {
    GetID() uuid.UUID
}

func GetByCollection(collectionName string, entries []Entry) {
    // This could be a lookup in a database or filesystem

    collections := map[string][]string{
        "books": []string{
            `{"ID": "c8cc718d-94a9-4605-a4bb-05d5aa067fd6", "Title": "Nils Holgersson", "Author": "d89e4a0a-6a65-4754-9090-f8b6c7d6eeec"}`,
            `{"ID": "46ad379e-17f2-4961-b615-d4301160f892", "Title": "Ronja rövardotter", "Author": "a1bba636-0700-474f-8fe8-2ad3ec9d061c"}`,
        },
        "authors": []string{
            `{"ID": "d89e4a0a-6a65-4754-9090-f8b6c7d6eeec", "Name": "Selma Lagerlöf"}`,
            `{"ID": "a1bba636-0700-474f-8fe8-2ad3ec9d061c", "Name": "Astrid Lindgren"}`,
        },
    }

    if collections[collectionName] != nil {
        for _, entryData := range collections[collectionName] {
            entry := BaseEntry{}
            json.Unmarshal([]byte(entryData), &entry)
            *entries = append(*entries, &entry)
        }
    }
}

以及我尝试使用它的测试:

    package temp_test

    import (
        "testing"

        "github.com/mojlighetsministeriet/next/temp"
        uuid "github.com/satori/go.uuid"
        "github.com/stretchr/testify/assert"
    )

    type Book struct {
        temp.BaseEntry
    }

    func TestPopulate(test *testing.T) {
        books := []Book{}
        temp.GetByCollection("books", &books)
        assert.NotEqual(test, uuid.Nil, books[0].GetID())
    }

取决于我声明的是 GetByCollection(collectionName string, entries []Entry) 还是 GetByCollection(collectionName string, entries *[]Entry) 我得到:

# github.com/mojlighetsministeriet/next/temp
./main.go:39:4: invalid indirect of entries (type []Entry)

或

# github.com/mojlighetsministeriet/next/temp_test
./main_test.go:17:32: cannot use &books (type *[]Book) as type * 
[]temp.Entry in argument to temp.GetByCollection

我应该如何编写才能通过调用 GetByCollection 来选择条目类型，比如要填充的 []Book 或 []Author slice ？

我可能需要以某种方式重构，最后我喜欢类似于 GORM 的查询方法 ( http://gorm.io/docs/query.html#Query ) db.Find(&users) 但喜欢 GetByCollection("books", &books)

最佳答案

需要反射才能处理不同的 slice 类型。方法如下:

func GetByCollection(collectionName string, result interface{}) {    
    collections := map[string][]string{
        "books": []string{
            `{"ID": "c8cc718d-94a9-4605-a4bb-05d5aa067fd6", "Title": "Nils Holgersson", "Author": "d89e4a0a-6a65-4754-9090-f8b6c7d6eeec"}`,
            `{"ID": "46ad379e-17f2-4961-b615-d4301160f892", "Title": "Ronja rövardotter", "Author": "a1bba636-0700-474f-8fe8-2ad3ec9d061c"}`,
        },
        "authors": []string{
            `{"ID": "d89e4a0a-6a65-4754-9090-f8b6c7d6eeec", "Name": "Selma Lagerlöf"}`,
            `{"ID": "a1bba636-0700-474f-8fe8-2ad3ec9d061c", "Name": "Astrid Lindgren"}`,
        },
    }

    slice := reflect.ValueOf(result).Elem()
    elementType := slice.Type().Elem()

    for _, entryData := range collections[collectionName] {
        v := reflect.New(elementType)
        json.Unmarshal([]byte(entryData), v.Interface())
        slice.Set(reflect.Append(slice, v.Elem()))
    }
}

这样调用它:

var books []Book
GetByCollection("books", &books)

Playground example

关于go - 如何填充作为函数引用传递的接口(interface)片段，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/50783071/