Another idea is to have wire.Subtract be a wire directive, used to wrap a ProviderSet in a wire.NewSet or a wire.Build.

Use cases might be:

1. I want to make a Set AB that unions 2 other sets A and B, but there's a type T that's the same between A and B.

var SetAB = wire.NewSet(A, B)

• Today, you'd get an error that there's two providers for T and you'd be kind of hosed.
• With wire.Subtract, you could do:

var SetAB = wire.NewSet(A, wire.Subtract(B, T))

2. I want to use an existing ProviderSet, but want to override one of the types it provides. For example, azureblob defines a Set that has NewPipeline and Options{} in it. Today, this code would produce an error because Options is provided twice, once by the injector function parameter and once by azureblob.Set.

func azureBucket(bucketName string, opts *azureblob.Options) *blob.Bucket {
  wire.Build(
    azureblob.DefaultIdentity,
    azureblob.Set,
  )

Again, you'd be kind of hosed; you'd have to explicitly add all of the providers in azureblob.Set that you need. With wire.Subtract, you would do:

func azureBucket(bucketName string, opts *azureblob.Options) *blob.Bucket {
  wire.Build(
    azureblob.DefaultIdentity,
    wire.Subtract(azureblob.Set, azureblob.Options),
  )

@zombiezen Any chance this will be worked on? Will a PR be accepted if I implement this? This one seems useful for mocking purpose for me.

I have same issue here, Just want to change the timeout value in the default server's driver. :(

This seems reasonable to me, but I haven't been working on Wire for a while. @vangent, WDYT?

@eliben can you add the new owners for this repo?

wire.Subtract sounds good, I'm happy to help review and merge a PR (new owner here :D)