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Add HandlerFunc generics support #477

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Add HandlerFunc generics support #477

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17 changes: 13 additions & 4 deletions lambda/entry_generic.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,15 +9,24 @@ import (
"context"
)

// HandlerFunc represents a valid input with two arguments and two returns as described by Start
// HandlerFunc represents a valid input with arguments and returns as described by Start
type HandlerFunc[TIn, TOut any] interface {
func(context.Context, TIn) (TOut, error)
~func(context.Context, TIn) (TOut, error) |
~func() |
~func(TIn) |
~func() error |
~func(TIn) error |
~func() (TOut, error) |
~func(TIn) (TOut, error) |
~func(context.Context) |
~func(context.Context) error |
~func(context.Context) (TOut, error) |
~func(context.Context, TIn) |
~func(context.Context, TIn) error
}

// StartHandlerFunc is the same as StartWithOptions except that it takes a generic input
// so that the function signature can be validated at compile time.
//
// Currently only the `func (context.Context, TIn) (TOut, error)` variant is supported
func StartHandlerFunc[TIn any, TOut any, H HandlerFunc[TIn, TOut]](handler H, options ...Option) {
start(newHandler(handler, options...))
}
2 changes: 1 addition & 1 deletion lambda/entry_generic_test.go
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Expand Up @@ -21,7 +21,7 @@ func TestStartHandlerFunc(t *testing.T) {
}

f := func(context.Context, any) (any, error) { return 1, nil }
StartHandlerFunc(f)
StartHandlerFunc[any, any](f)
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this is a breaking change, as the go compiler isn't smart enough to infer the types when more than one variant is added to the interface. See prior discussion: #468 (comment)

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I see, thank you for considering this @bmoffatt !
I am still wondering if we can add this changes by adding another function (let's say StartTypedHandlerFunc for now)that accepts "any" type and it calls StartHandlerFunc[any, any](f).
There will be no type-safe though, but user does not need to specify types for StartHandlerFunc . instead, they may want to use new StartHandlerTypedFunc that supports generics with type parameter.

Sorry my English is not good enough to explain this, hope it works!


assert.Equal(t, "expected AWS Lambda environment variables [_LAMBDA_SERVER_PORT AWS_LAMBDA_RUNTIME_API] are not defined", actual)

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