return []error rather than error

Concurrent functions return multiple errors.
These are now returned only as either a channel or a slice.

This avoids a dependency on a 3rd party multi errors library.
The standard library errors.Join is awkward to use because
there is not a simple way to unwrap the errors.

We could use a custom multi error.
However, to make this convenient to use it should be returned as a
pointer to the struct rather than an opaque error.
But Go has a subtle design issue where
an interface can end up being non-nil when storing a pointer to a struct.

Returning []error still allows the caller to use errors.Join() if they don't
care about iterating the individual errors.

The main issue is that someone may check != nil rather than len > 0
However, all the APIs are designed to return nil rather than a zero
length slice.

Additionally, don't use the default recovery handler.
Write more errors to the error channels.
Panic a few errors that shouldn't happen.

README.md

@@ -17,12 +17,10 @@ parallelism in Go using generics
 
 ## Error handling
 
-This library relies on go-recovery to trap panics that occur in go routines.
-go-recovery by default will log panics but can be configured to send them to an error monitoring service.
+This library relies on go-recovery to trap panics that occur in user supplied work functions.
+This library does have unhandled panics, but only in places where panics should never occur.
+Errors and panics are written to an error channel for maximum flexibility.
+There are helpers for common patterns for dealing with errors:
 
-For maximum flexibility with error handling, many of the parallel functions return an error channel.
-Any errors that occur in work functions will be put into the error channel.
-There are helpers for common patterns for dealing with the errors:
-
-* CollectErrors
-* CancelAfterFirstError
+* CollectErrors (wait and convert to a slice)
+* CancelAfterFirstError (cancel and wait and convert to a slice)

go.mod

@@ -5,13 +5,11 @@ go 1.19
 require (
 	github.com/gregwebs/go-recovery v0.2.1
 	github.com/stretchr/testify v1.8.1
-	go.uber.org/multierr v1.9.0
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/gregwebs/errors v1.1.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	go.uber.org/atomic v1.7.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -10,15 +10,10 @@ github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZN
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
 github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
-github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
 github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
-go.uber.org/atomic v1.7.0 h1:ADUqmZGgLDDfbSL9ZmPxKTybcoEYHgpYfELNoN+7hsw=
-go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
-go.uber.org/multierr v1.9.0 h1:7fIwc/ZtS0q++VgcfqFDxSBZVv/Xo49/SYnDFupUwlI=
-go.uber.org/multierr v1.9.0/go.mod h1:X2jQV1h+kxSjClGpnseKVIxpmcjrj7MNnI0bnlfKTVQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=