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| 187 | The semantics of stringref tags require the decoder to be aware and the |
187 | The semantics of stringref tags require the decoder to be aware and the |
| 188 | encoder to be under control of the sequence in which data items are |
188 | encoder to be under control of the sequence in which data items are |
| 189 | encoded into the CBOR stream. This means these tags cannot be implemented |
189 | encoded into the CBOR stream. This means these tags cannot be implemented |
| 190 | on top of every generic CBOR encoder/decoder (which might reorder entries |
190 | on top of every generic CBOR encoder/decoder (which might reorder entries |
| 191 | in a map); they typically need to be integrated into their works. |
191 | in a map); they typically need to be integrated into their works. |
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192 | |
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193 | =head2 DESIGN RATIONALE |
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194 | |
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195 | The stringref tag was chosen to be short, without requiring standards |
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196 | action. The namespace tag is rare, so doesn't benefit from a short |
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197 | encoding as much. |
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198 | |
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199 | Implicit tagging/counting was chosen to support stream encoders. Having |
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200 | to tag strings first requires either multiple passes over the data (which |
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201 | might not be available, ruling out some encoders) or tagging more strings |
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202 | than needed (wasting space). Explicit tagging also isn't necessarily |
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203 | better even under optimal conditions, as the explicit tags waste space. |
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204 | |
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205 | Stream decoders are affected less by implicit tagging than encoders. |
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206 | |
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207 | The namespace tag was introduced for two reasons: first to allow embedding |
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208 | of CBOR strings into other CBOR strings, secondly for decoding efficiency |
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209 | - the decoder only has to expect stringref tags inside namespaces and |
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210 | therefore doesn't have to maintain extra state outside of them. |
| 192 | |
211 | |
| 193 | =head1 EXAMPLES |
212 | =head1 EXAMPLES |
| 194 | |
213 | |
| 195 | The array-of-maps from the rationale example would normally compress to a |
214 | The array-of-maps from the rationale example would normally compress to a |
| 196 | CBOR text of 83 bytes. Using this extension where possible, this reduces |
215 | CBOR text of 83 bytes. Using this extension where possible, this reduces |
