proto3 scalar 标量
Scalar Value Types
| .proto Type | Go Type | PHP Type |
| double | float64 | float |
| float | float32 | float |
| int32 | int32 | integer |
| int64 | int64 | integer/string |
| unit32 | uint32 | integer |
| unit64 | uint64 | integer/string |
| sint32 | int32 | integer |
| sint64 | int64 | integer/string |
| fixed32 | unit32 | integer |
| fixed64 | unit64 | integer/string |
| sfixed32 | int32 | integer |
| sfixed64 | int64 | integer/string |
| bool | bool | boolean |
| string | string | string |
| bytes | []byte | string |
