mirror of
https://github.com/protocolbuffers/protobuf-go.git
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81 lines
2.5 KiB
Go
81 lines
2.5 KiB
Go
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// Copyright 2024 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package proto
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// ValueOrNil returns nil if has is false, or a pointer to a new variable
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// containing the value returned by the specified getter.
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//
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// This function is similar to the wrappers (proto.Int32(), proto.String(),
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// etc.), but is generic (works for any field type) and works with the hasser
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// and getter of a field, as opposed to a value.
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//
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// This is convenient when populating builder fields.
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//
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// Example:
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//
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// hop := attr.GetDirectHop()
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// injectedRoute := ripb.InjectedRoute_builder{
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// Prefixes: route.GetPrefixes(),
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// NextHop: proto.ValueOrNil(hop.HasAddress(), hop.GetAddress),
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// }
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func ValueOrNil[T any](has bool, getter func() T) *T {
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if !has {
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return nil
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}
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v := getter()
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return &v
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}
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// ValueOrDefault returns the protobuf message val if val is not nil, otherwise
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// it returns a pointer to an empty val message.
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//
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// This function allows for translating code from the old Open Struct API to the
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// new Opaque API.
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//
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// The old Open Struct API represented oneof fields with a wrapper struct:
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//
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// var signedImg *accountpb.SignedImage
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// profile := &accountpb.Profile{
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// // The Avatar oneof will be set, with an empty SignedImage.
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// Avatar: &accountpb.Profile_SignedImage{signedImg},
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// }
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//
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// The new Opaque API treats oneof fields like regular fields, there are no more
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// wrapper structs:
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//
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// var signedImg *accountpb.SignedImage
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// profile := &accountpb.Profile{}
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// profile.SetSignedImage(signedImg)
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//
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// For convenience, the Opaque API also offers Builders, which allow for a
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// direct translation of struct initialization. However, because Builders use
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// nilness to represent field presence (but there is no non-nil wrapper struct
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// anymore), Builders cannot distinguish between an unset oneof and a set oneof
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// with nil message. The above code would need to be translated with help of the
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// ValueOrDefault function to retain the same behavior:
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//
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// var signedImg *accountpb.SignedImage
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// return &accountpb.Profile_builder{
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// SignedImage: proto.ValueOrDefault(signedImg),
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// }.Build()
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func ValueOrDefault[T interface {
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*P
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Message
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}, P any](val T) T {
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if val == nil {
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return T(new(P))
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}
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return val
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}
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// ValueOrDefaultBytes is like ValueOrDefault but for working with fields of
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// type []byte.
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func ValueOrDefaultBytes(val []byte) []byte {
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if val == nil {
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return []byte{}
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}
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return val
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}
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