Destructors about inject

[yoyofx]

I think used interface better. such as IDestruct interface has a OnDestruct method.

[defval]

@maxzhang1985 I'd prefer to separate the object lifecycle management functions from the object functionality. Also, interface forces to wrapping standard library types.

I start to implement the Provider interface in v2 for advanced providing. Maybe, extended ProviderDestructor or ProviderCloser interface will be the best option.

type Provider interface {
    Identity() Identity
    Construct() (interface, error)
}

type ProviderDestructor interface {
    Destruct() error
}

I didn't have time to test it. But here a usage example.

I'm still thinking about it.

[defval]

I came to the conclusion that a better option is to support an optional cleanup function as a result of the constructor (like in google/wire).

For example:

func provideFile(log Logger, path Path) (*os.File, func(), error) {
    f, err := os.Open(string(path))
    if err != nil {
        return nil, nil, err
    }
    cleanup := func() {
        if err := f.Close(); err != nil {
            log.Log(err)
        }
    }
    return f, cleanup, nil
}

[defval]

Implemented in #26