This rule is part of MISRA C++:2023.
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Rule 8.3.2 - The built-in unary + operator should not be used
[expr.unary.op] / 7
Category: Advisory
Analysis: Decidable,Single Translation Unit
Rationale
The built-in unary + operator triggers integral promotion, but otherwise performs no other operation. When its operand is a function
name or lambda, decay to a function pointer is triggered. The use of static_cast is recommended instead as it makes it clear that these
conversions are present.
Example
auto x = + u8a; // Non-compliant - triggers promotion to int
auto pf = +[](){}; // Non-compliant - pf is a void(*)()
x = +1; // Non-compliant
x =+ 1; // Non-compliant - unary +, not +=
enum A : uint8_t { one };
enum B : uint8_t { two };
uint8_t operator+( B b ) { return b; }
auto a = +one; // Non-compliant
auto b = +two; // Rule does not apply
auto c = operator+( two ); // Rule does not apply
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