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Re: Why enum is automatically converted in class member but not in global function

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On 05/12/2019 01:57, Bo Persson wrote:
> On 2019-12-05 at 01:53, JiiPee wrote:
>> I wonder why the compiler does automatic type conversion for an enum 
>> to int if the function is a class member, but does not do that if the 
>> function is a global function.
>>
>> Example code:
>>
>> enum MyEnum
>> {
>> enumVal1
>> }
>>
>>
>> 1)
>> += as a class member:
>>
>> template <typename T>
>> inline void MyClass<T>::operator += (const T& val)
>> {
>> }
>>
>> MyClass<int> obj;
>> obj += enumVal1; // converts enumVal1 to int and calls operator +=
>>
>> This all works.
>>
>> 2)
>>
>> The same += as a global function:
>>
>> template <typename T>
>> inline void operator += (const MyClass<T>& obj, const T& val)
>> {
>> }
>>
>> obj += enumVal1; // does not convert enumVal1 to int
>>
>> This one does not compile, I get this error:
>> "+= does not define this operator or a conversion to a type 
>> acceptable to the predefined operator"
>>
>>
>
> It has to do with the order of type deduction and overload resolution. 
> Type deduction is always performed first.
>
> In the first case, T is given from the use of MyClass<int>. That class 
> instantiation has a member operator that takes an int, and the enum is 
> convertible to int. Good.
>
>
> In the second case, the compiler is looking for an operator that takes 
> a class object and an enum value. There isn't any.
>
> The fact that the enum might be convertible to some other type that 
> would match the template doesn't help, as type deduction is performed 
> first and enumVal1 just isn't a T. So that template is not added to 
> the potential overload set.
>
>

ok, thanks. A little difficult to google these issues, thats why asked 
here :)

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Why enum is automatically converted in class member but not in global function JiiPee <no@notvalid.com> - 2019-12-05 00:53 +0000
  Re: Why enum is automatically converted in class member but not in global function Bo Persson <bo@bo-persson.se> - 2019-12-05 02:57 +0100
    Re: Why enum is automatically converted in class member but not in global function JiiPee <no@notvalid.com> - 2019-12-05 14:21 +0000

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