Delayed error checking

[wirekang]

I use this function personally. With this, you can save dozens of lines with if err != nil. Execute all simple logics (doSimpleThing) first, and check the error later. The error will be the first occured error or nil.

func Delay[T any](target *error) func(v T, err error) T {
	a := func(v T, err error) T {
		if *target == nil && err != nil {
			*target = err
		}
		return v
	}
	return a
}

Example:

func doSimpleThing1() (int, error){...}
func doSimpleThing2() (string, error){...}

var err error

dInt := Delay[int](&err)
dString := Delay[string](&err)

_ = complexStruct{
    id: dInt(doSimpleThing1()),
    name: dString(doSimpleThing2()),
    email: dString(doSimpleThing2()),
    ...
}

// check error later
if err != nil {
    panic(err)
}

I think this function is appropriate for this package if there's a good name for it. Do you have a good idea?

[samber]

You use case is interesting.

I wonder if it could be replaced by Must+Try:

err, ok := lo.TryWithErrorValue(func() error {
    complexStruct{
        id: Must(doSimpleThing1()),
        name: Must(doSimpleThing2()),
        email: Must(doSimpleThing2()),
        ...
    }

    return nil
})

WDYT?

[wirekang]

@samber
https://gist.github.com/wirekang/372054026f5f7db887d55485b8ee4ca2

I wrote 3 different way to make Person from ctx. I think Delay(temp name) way is also a decent way, although it's similar with Try way.

[samber]

Using this Delay function implies a side effect. I'm not a fan of such a pattern. In the library, we try to stay close to functional programming philosophy.

On the other side, Try+Must will halt the function and immediately return the error.

I don't want to block this contrib, but I wonder if we could make it easier to use.

[wirekang]

I totally agree with you, and I think there are no way to make the function easier to use due to limitation of Go.