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Niels LohmannandAfonso Januário
a5f5d3059b
* Make std::hash<basic_json> consistent with operator== for numbers operator== converts between number_integer, number_unsigned, and number_float before comparing, so json(0), json(0U), and json(0.0) all compare equal. hash() folded the specific value_t into the result for each of the three numeric cases, giving each a distinct hash and breaking the standard Hash requirement that a == b implies hash(a) == hash(b). A std::unordered_set could therefore hold all three as separate elements even though they compare equal. hash() now treats all three numeric variants the same way: it converts the value to number_float_t and combines it with a single shared type tag, so any two numbers operator== considers equal hash identically regardless of which internal type actually holds them. Updated the accompanying test to check this consistency directly (including via an actual unordered_set) instead of asserting that 0, 0U, and 0.0 hash differently, since that assumption was the bug. Also corrected the function's own doc comment and the std::hash API docs, which described the old behavior as intended. Fixes #5400 Signed-off-by: Afonso Januário <afonso-januario@hotmail.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Remove now-unused number_integer_t/number_unsigned_t typedefs in hash() Merging the three numeric branches into one that only reads number_float_t left these two aliases unused, which several CI configurations treat as a build error under -Wunused-local-typedefs. Signed-off-by: Afonso Januário <afonso-januario@hotmail.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Mark the unordered_set in the hash regression test const clang-tidy's misc-const-correctness check flagged it: the set is never mutated after construction, only read via size(). Signed-off-by: Afonso Januário <afonso-januario@hotmail.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Normalize -0.0 in number hashes and test range ends operator== compares numbers exactly since #5459, so equal numbers share one value and convert to the same number_float_t. Update the comment accordingly, map -0.0 to 0.0 before hashing (std::hash need not do that), and test -0.0 and the ends of the integer ranges. Show hash(0.0) in the docs example and note the change in the version history. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Clarify hash documentation after review - Say "may hash differently" for null, false, and numbers, since a collision across types is possible. - Name the storage types (signed integer, unsigned integer, floating-point number) instead of example literals. - Explain that the hash survives converting an integer to number_float_t but not the lossy conversion back, and that unequal numbers may share a hash. - State that the example hash values are illustrative only and vary by platform, compiler, compiler version, and library version. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Afonso Januário <afonso-januario@hotmail.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me> Co-authored-by: Afonso Januário <afonso-januario@hotmail.com>