Add Marshaler and Unmarshaler interfaces #17
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Add Marshaler and Unmarshaler interfaces, which allow for custom encoding/decoding
working similarly to encoding/json Marshaler and Unmarshaler:
```
type Marshaler interface {
MarshalXDR(e *Encoder) (int, error)
}
type Unmarshaler interface {
UnmarshalXDR(e *Decoder) (int, error)
}
```
The Decoder and Encoder automatically call the relevant methods if found.
Both implementation by value and by pointer are supported.
A new error (`ErrCustomUnaddressableByPointer`) will be returned if
a by-pointer implementation is found but the value passed is unaddressable
(not allowing to call the method by pointer).
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bartekn
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Nov 10, 2021
| @@ -770,6 +776,37 @@ func (d *Decoder) decodeInterface(v reflect.Value) (int, error) { | |||
| return d.decode(ve, 0) | |||
| } | |||
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| func getUnmarshaler(ve reflect.Value) Unmarshaler { | |||
| // Check the type first to avoid an unnecessary allocation when casting to interface | |||
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Is type switch also allocating? I wonder if can avoid using reflect (which usually is slow). See: https://stackoverflow.com/a/28027945/9812359 maybe we can add a small benchmark to check it out. I think, it can simplify the code a bit.
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From the tests I performed, I don't think it allocates.
| @@ -1013,6 +1063,13 @@ func (d *Decoder) decodePtr(v reflect.Value) (int, error) { | |||
| return n, err | |||
| } | |||
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| // We intentionally check for Marshaler before deferencing the pointer. | |||
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Suggested change
| // We intentionally check for Marshaler before deferencing the pointer. | |
| // We intentionally check for Unmarshaler before deferencing the pointer. |
| @@ -1013,6 +1063,13 @@ func (d *Decoder) decodePtr(v reflect.Value) (int, error) { | |||
| return n, err | |||
| } | |||
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| // We intentionally check for Marshaler before deferencing the pointer. | |||
| // This is because, for unaddressable values, you cannot recover the | |||
| // pointer later on, which would make impossible to invoke by-address marshalers. | |||
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Suggested change
| // pointer later on, which would make impossible to invoke by-address marshalers. | |
| // pointer later on, which would make impossible to invoke by-address unmarshalers. |
|
I think I am going to close this, because after updating xdrgen to generate Using by-value invocations, can (and does) cause allocations, which impacts performance quite negatively. See stellar/xdrgen#67 (comment) for more details. |
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Add Marshaler and Unmarshaler interfaces, which allow for custom encoding/decoding
working similarly to
encoding/jsonMarshaler and Unmarshaler:The Decoder and Encoder automatically call the relevant methods if found.
Both implementation by value and by pointer are supported.
A new error (
ErrCustomUnaddressableByPointer) will be returned ifa by-pointer implementation is found but the value passed is unaddressable
(not allowing to call the method by pointer).
Note that
Marshaleris intended to override theEncodeTomethods introduced at stellar/go#3957 . I will later update xdrgen to generateMarshalXDRimplementations instead.