在Golang中使用sql.NullFloat64与* float64？

Question

I'm using gorm to define my db table schema. Noticed that gorm itself uses time.Time for created_at and *time.Time for deleted_at. I'm assuming this is because deleted_at has cases of being NULL.

I also noticed that for many Golang ORMs they use sql.NullFloat64 for storing db values that could be a float64 or NULL. Why not just use *float64 instead of sql.NullFloat64? What's the difference?

type Geo struct {
    latitude *float64
    longitude sql.NullFloat64
}
// What is the difference between latitude and longitude in this case?

Answer 1

From Russ Cox (biggest Go's contributor according to Github) : https://groups.google.com/forum/#!topic/golang-nuts/vOTFu2SMNeA

There's no effective difference. We thought people might want to use NullString because it is so common and perhaps expresses the intent more clearly than *string. But either will work.

I'm thinking though that using a pointer might give the GC one more thing to track. It probably depends on the usage.

On some very simple code, using -gcflags=-m to build, the escape analysis does say that new(float64) escapes to heap (here is the dummy code I used: https://play.golang.org/p/K4sQaXyQKG).

Also, when debugging, printing a struct containing a sql.NullSomething ({value:{Float64:1 Valid:true}}) looks better than a struct containing a pointer ({value:0xc82000a420}).

So I'd recommend the usage of the sql.Null* structs.