Cloning injectors with registered services

[suzuki-safie]

Cloning dependency container would be useful for unit testing.
User can reuse production service registrations and replace some service to mock service.

example:

var injector *do.Injector;
func init() {
    do.Provide[Service](injector, func (i *do.Injector) (Service, error) {
        return &RealService{}, nil
    })
    do.Provide[*App](injector, func (i *do.Injector) (*App, error) {
        return &App{i.MustInvoke[Service](i)}, nil
    })
}

func TestService(t *testing.T) {
    i := injector.Clone()
    defer i.Shutdown()
    // replace Service to MockService
    do.Provide[Service](i, func (i *do.Injector) (Service, error) {
        return &MockService{}, nil
    }))
    app := do.Invoke[*App](i)
    // do unit testing with mocked service
}

This usecase is relying on service-overriding behavior and inconsistent with #1 , so it would be nice if service-overriding behavior is officially supported.

[samber]

Hi @suzuki-safie and thanks for your contribution.

I like the idea of cloning+overriding injectors for tests, especially for mocks!

But I'm not really sure service overriding should be enabled by default. Such a design might lead to dangerous behavior for lazy loaded services.

I'm thinking about 2 alternatives:

• A do.Replace[T](*do.Injector, func (*do.Injector) (T, error)) helper, similar to do.Provide
• An option to injector constructor: do.NewWithOpts(&do.InjectorOpts{ AllowServiceOverride: true })

The second option seems better.

WDYT?

[codecov-commenter]

Codecov Report

Merging #6 (5778c8a) into master (2afdbc0) will decrease coverage by 0.69%.
The diff coverage is 80.76%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
- Coverage   91.35%   90.65%   -0.70%     
==========================================
  Files           6        6              
  Lines         370      396      +26     
==========================================
+ Hits          338      359      +21     
- Misses         24       28       +4     
- Partials        8        9       +1     

Flag	Coverage Δ
unittests	90.65% <80.76%> (-0.70%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
service.go	88.88% <ø> (ø)
service_eager.go	65.21% <0.00%> (-6.22%)	⬇️
injector.go	92.57% <81.25%> (-1.14%)	⬇️
service_lazy.go	89.85% <100.00%> (+1.33%)	⬆️

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[suzuki-safie]

A do.Replace[T](*do.Injector, func (*do.Injector) (T, error)) helper, similar to do.Provide

I like this option. I think do.Replace(...) expresses it's intent more clearly.

[samber]

Why did you close this PR ? :-(

Sorry for the late reply, I am a little bit busy. The SaaS industry is catching fire. 🔥 😬

[suzuki-safie]

@samber
Sorry, I didn't have enough time to do this PR.
Thank you for merging!