Commit 8acb79fc5ecde0ca8a06e9cbcd628f8672d00417
1 parent
1faa2150
Remove notes on safe QPDFObjectHandle -- not worth doing
The impact on the code would be extremely high, and using it would
clutter the code greatly because it would break chaining like
a.getKey("/B").getKey("/C"). There are better ways to deal with the
issue.
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TODO
| @@ -4,62 +4,6 @@ Documentation | @@ -4,62 +4,6 @@ Documentation | ||
| 4 | * See #530 -- add an appendix explaining PDF encryption in general | 4 | * See #530 -- add an appendix explaining PDF encryption in general |
| 5 | plus how it's handled by qpdf. | 5 | plus how it's handled by qpdf. |
| 6 | 6 | ||
| 7 | -Safer QPDFObjectHandle | ||
| 8 | -====================== | ||
| 9 | - | ||
| 10 | -Consider one of the following or something similar to make it possible | ||
| 11 | -to completely eliminate warnings from treating objects of one type as | ||
| 12 | -objects of a different type. | ||
| 13 | - | ||
| 14 | -Modeled after rust's Option type: | ||
| 15 | - | ||
| 16 | -``` | ||
| 17 | -QPDFSafeObjectHandle soh = getObjectFromSomewhere(); | ||
| 18 | - | ||
| 19 | -// QPDFSafeObjectHandle would be just like QPDFObjectHandle except | ||
| 20 | -// none of the type-specific methods would be there. | ||
| 21 | -QPDFDictionaryHandle dh = soh.asDictionary(); | ||
| 22 | -if (dh.isValid()) { | ||
| 23 | - QPDFSafeObjectHandle value = dh.value().getKey("/Key"); | ||
| 24 | -} | ||
| 25 | -``` | ||
| 26 | - | ||
| 27 | -More like typescript's narrowing: | ||
| 28 | - | ||
| 29 | -``` | ||
| 30 | -QPDFSafeObjectHandle soh = getObjectFromSomewhere(); | ||
| 31 | -QPDFSafeObjectHandle value = soh.getKey("/Key"); | ||
| 32 | -``` | ||
| 33 | - | ||
| 34 | -this would raise `std::logic_error` even if soh was a dictionary. But this would work: | ||
| 35 | - | ||
| 36 | -``` | ||
| 37 | -QPDFSafeObjectHandle soh = getObjectFromSomewhere(); | ||
| 38 | -if (soh.isDictionary()) { | ||
| 39 | - QPDFSafeObjectHandle value = soh.getKey("/Key"); | ||
| 40 | -} | ||
| 41 | -``` | ||
| 42 | - | ||
| 43 | -In safe mode, we would have checkers (like we do now) but we would | ||
| 44 | -track whether a specific checker had been called and throw a | ||
| 45 | -`std::logic_error` if we call a type-specific method without first | ||
| 46 | -calling a checker. This means that code that passes the happy path | ||
| 47 | -still has to always do type checks, and this should completely | ||
| 48 | -eliminate type mismatch warnings. | ||
| 49 | - | ||
| 50 | -Migrating existing code to use this safe version would just be a | ||
| 51 | -matter of changing all occurrences of `QPDFObjectHandle` to | ||
| 52 | -`QPDFSafeObjectHandle` and making sure you had test coverage on every | ||
| 53 | -accessor/mutator method call. If you did and the code worked for the | ||
| 54 | -happy path, then you would be assured of never getting a warning about | ||
| 55 | -the a method called on an object of the wrong type. | ||
| 56 | - | ||
| 57 | -Implementation idea: maybe make a QPDFObjectHandleInternal<bool safe> | ||
| 58 | -template with QPDFObjectHandle as QPDFObjectHandleInternal<false> and | ||
| 59 | -QPDFSafeObjectHandle as QPDFObjectHandle<true>. We could then | ||
| 60 | -potentially specialize certain methods to reduce the overhead and code | ||
| 61 | -duplication without causing a change to the behavior of any existing | ||
| 62 | -code. | ||
| 63 | 7 | ||
| 64 | Document-level work | 8 | Document-level work |
| 65 | =================== | 9 | =================== |