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Fix C++20/gcc-12 issues (Part 2) (#3446)

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* Add C++20 3-way comparison operator and fix broken comparisons

Fixes #3207.
Fixes #3409.

* Fix iterators to meet (more) std::ranges requirements

Fixes #3130.
Related discussion: #3408

* Add note about CMake standard version selection to unit tests

Document how CMake chooses which C++ standard version to use when
building tests.

* Update documentation

* CI: add legacy discarded value comparison

* Fix internal linkage errors when building a module
This commit is contained in:
Florian Albrechtskirchinger
2022-05-29 13:08:06 +02:00
committed by GitHub
parent ede6667858
commit 6b97599a27
35 changed files with 1963 additions and 690 deletions
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docs/mkdocs/docs/api/basic_json/operator_ne.md
+33 -6
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@@ -1,16 +1,32 @@
# <small>nlohmann::basic_json::</small>operator!=
```cpp
bool operator!=(const_reference lhs, const_reference rhs) noexcept;
// until C++20
bool operator!=(const_reference lhs, const_reference rhs) noexcept; // (1)
template<typename ScalarType>
bool operator!=(const_reference lhs, const ScalarType rhs) noexcept;
bool operator!=(const_reference lhs, const ScalarType rhs) noexcept; // (2)
template<typename ScalarType>
bool operator!=(ScalarType lhs, const const_reference rhs) noexcept;
bool operator!=(ScalarType lhs, const const_reference rhs) noexcept; // (2)
// since C++20
class basic_json {
bool operator!=(const_reference rhs) const noexcept; // (1)
template<typename ScalarType>
bool operator!=(ScalarType rhs) const noexcept; // (2)
};
```
Compares two JSON values for inequality by calculating `#!cpp !(lhs == rhs)`.
1. Compares two JSON values for inequality according to the following rules:
- The comparison always yields `#!cpp false` if (1) either operand is discarded, or (2) either
operand is `NaN` and the other operand is either `NaN` or any other number.
- Otherwise, returns the result of `#!cpp !(lhs == rhs)` (until C++20) or
`#!cpp !(*this == rhs)` (since C++20).
2. Compares a JSON value and a scalar or a scalar and a JSON value for inequality by converting the
scalar to a JSON value and comparing both JSON values according to 1.
## Template parameters
@@ -27,7 +43,7 @@ Compares two JSON values for inequality by calculating `#!cpp !(lhs == rhs)`.
## Return value
whether the values `lhs` and `rhs` are not equal
whether the values `lhs`/`*this` and `rhs` are not equal
## Exception safety
@@ -37,6 +53,16 @@ No-throw guarantee: this function never throws exceptions.
Linear.
## Notes
!!! note "Comparing `NaN`"
`NaN` values are unordered within the domain of numbers.
The following comparisons all yield `#!cpp false`:
1. Comparing a `NaN` with itself.
2. Comparing a `NaN` with another `NaN`.
3. Comparing a `NaN` and any other number.
## Examples
??? example
@@ -69,4 +95,5 @@ Linear.
## Version history
- Added in version 1.0.0.
1. Added in version 1.0.0. Added C++20 member functions in version 3.11.0.
2. Added in version 1.0.0. Added C++20 member functions in version 3.11.0.