8000 dynamic.h operator== claiming to do a deep equal comparison but its not · Issue #2424 · facebook/folly · GitHub
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dynamic.h operator== claiming to do a deep equal comparison but its not #2424

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hannojg opened this issue Apr 24, 2025 · 1 comment
Open

dynamic.h operator== claiming to do a deep equal comparison but its not #2424

hannojg opened this issue Apr 24, 2025 · 1 comment

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@hannojg
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hannojg commented Apr 24, 2025

In the json/dynamic.h its saying that the equal operator will do a deep equal comparison:

folly/folly/json/dynamic.h

Lines 293 to 301 in 08d6d55

/**
* Deep equality comparison. This will compare all the way down
* an object or array, and is potentially expensive.
*
* NOTE: Implicit conversion will be done between ints and doubles, so numeric
* equality will apply between those cases. Other dynamic value comparisons of
* different types will always return false.
*/
friend bool operator==(dynamic const& a, dynamic const& b);

but looking into the implementation if the types are matching its just comparing the address:

folly/folly/json/dynamic.cpp

Lines 119 to 131 in 08d6d55

bool operator==(dynamic const& a, dynamic const& b) {
if (a.type() != b.type()) {
if (a.isNumber() && b.isNumber()) {
auto& integ = a.isInt() ? a : b;
auto& doubl = a.isInt() ? b : a;
return integ.asInt() == doubl.asDouble();
}
return false;
}
#define FB_X(T) return *a.getAddress<T>() == *b.getAddress<T>();
FB_DYNAMIC_APPLY(a.type_, FB_X);
#undef FB_X

Maybe I am missing something but it seems to me that his is incorrect and no actual deep equal comparison? (I am looking for a built-in way to do a deep equal compare)
@yfeldblum
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This doesn't look like it compares addresses. *a.getAddress<T> is T&, not T*.

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@yfeldblum @hannojg
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