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This article mainly explains "how C++ defines overloaded operators in the namespace of operands". The explanation in this article is simple, clear and easy to learn and understand. let's study and learn how C++ defines overloaded operators in the namespace of operands.

C.168: define the overloaded operator in the namespace of the Operand

Reason (reason)

Readability. Provides the ability to use ADL discovery operators. Avoid inconsistencies in different namespaces.

Example (sample)

Struct S {}

Bool operator== (S, S); / / OK: in the same namespace as S, and even next to S

S s

Bool x = (s = s)

This is what the default equality comparison operator does, if there is such a default.

Example (sample)

Namespace N {

Struct S {}

Bool operator== (S, S); / / OK: in the same namespace as S, and even next to S

}

N::S s

Bool x = (s = = s); / / finds by ADL

Example, bad (negative example) struct S {}

S s

Namespace N {

S::operator! (sa) {return true;}

S not_s =! s

}

Namespace M {

S::operator! (sa) {return false;}

S not_s =! s

}

The meaning of! s in the N and M namespaces in the code is different. It's going to be very confusing. Removing the definition of namespace M will increase the likelihood of errors.

Note (Note)

If you define binocular operators for two different types in different namespaces, you cannot follow this guideline. For example:

Vec::Vector operator* (const Vec::Vector&, const Mat::Matrix&)

This is probably at its best.

See also (reference)

This can be said to be a special case of the rule that the helper should be defined in a namespace with the classes it helps.

Enforcement (implementation recommendations)

The tag does not have an operator defined in the same namespace as the Operand.

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