用一个数据处理库来泛型尝鲜

这是一个用 Go 实现的数据处理库，升级之前用 interface{}表示参数类型，阅读起来还是容易模糊。现在泛型出了之后，就把它升级一下：

原来：

// extract column from table // * First Argument:table // * Second Argument:column name result := query.Column(users, "UserID") userIDs := result.([]int) // generate a map from table,key is column value and value is it's row // * First Argument:table // * Second Argument:column name result = query.ColumnMap(users, "UserID") userMap := result.(map[int]User) // select data from table // * First Argument:table // * Second Argument:select rule result = query.Select(users, func(a User) Sex { if len(a.Name) >= 3 && a.Name[0:3] == "Man" { return Sex{IsMale: true} } return Sex{IsMale: false} }) sel := result.([]Sex) // filter data from table // * First Argument:table // * Second Argument:filter rule result = query.Where(users, func(a User) bool { if len(a.Name) >= 3 && a.Name[0:3] == "Man" { return true } return false }) where := result.([]User) // group data from table // * First Argument: left table // * Second Argument: group column name // * Third Argument: group rule result = query.Group(users, "UserID", func(users []User) Department { return Department{ Employees: users, } }) group := result.([]Department) // join data from two table ，support LeftJoin,RightJoin,InnerJoin 和 OuterJoin // * First Argument: left table // * Second Argument: right table // * Third Argument: join condition // * Forth Argument: join rule result = query.LeftJoin(admins, users, "AdminID = UserID", func(admin Admin, user User) AdminUser { return AdminUser{ AdminID: admin.AdminID, Level: admin.Level, Name: user.Name, CreateTime: user.CreateTime, } }) join := result.([]AdminUser) 

现在

// extract column from table // * First Argument:table // * Second Argument:column name userIDs := query.Column[User, int](users, "UserID") // []int // generate a map from table,key is column value and value is it's row // * First Argument:table // * Second Argument:column name userMap = query.ColumnMap[User, int, map[int]User](users, "UserID") // map[int]User // or usersMap = query.ColumnMap[User, int, map[int][]User](users, "[]UserID") // map[int][]User // select data from table // * First Argument:table // * Second Argument:select rule sel = query.Select(users, func(a User) Sex { if len(a.Name) >= 3 && a.Name[0:3] == "Man" { return Sex{IsMale: true} } return Sex{IsMale: false} }) // []Sex // filter data from table // * First Argument:table // * Second Argument:filter rule where = query.Where(users, func(a User) bool { if len(a.Name) >= 3 && a.Name[0:3] == "Man" { return true } return false }) // []User // group data from table // * First Argument: left table // * Second Argument: group column name // * Third Argument: group rule group = query.Group[User, Department, []Department](users, "UserID", func(users []User) Department { return Department{ Employees: users, } }) // []Department // or group = query.Group[User, []Department, *[]Department](users, "UserID", func(users []User) []Department { return []Department{ Employees: users, } }) // *[]Department // join data from two table ，support LeftJoin,RightJoin,InnerJoin 和 OuterJoin // * First Argument: left table // * Second Argument: right table // * Third Argument: join condition // * Forth Argument: join rule join = query.LeftJoin(admins, users, "AdminID = UserID", func(admin Admin, user User) AdminUser { return AdminUser{ AdminID: admin.AdminID, Level: admin.Level, Name: user.Name, CreateTime: user.CreateTime, } }) // []AdminUser 

减少了断言，还是挺好的。

一点问题

目前的 Go 泛型不支持类型参数内嵌，所以在 Group 函数里使用了指针。

// 这样是不行的 func Group[T, E any, R E | []E](data []T, groupType string, groupFunctor func([]T) E) R // 只好写成这样 func Group[T, E any, R *E | []E](data []T, groupType string, groupFunctor func([]T) E) R