On Tue, Mar 4, 2025 at 4:03 PM Tymi via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> Generally I wanted [[pure]] to be a combination of both [[unsequenced]]
> and [[reproducible]].
>
As Jan Schultke has pointed out in his SO answer, [[unsequenced]] implies
[[reproducible]].

>
> On Tue, 4 Mar 2025, 11:20 Tymi, <tymi.cpp_at_[hidden]> wrote:
>
>> I somehow didn't see your reply until now.
>>
>> Yes, you may call other pure functions from a pure function. I think it
>> also might be okay to call constexpr/consteval functions as well.
>>
>>
>> No, you may not call a function that could have side effects from a pure
>> function. That could be ill-formed, no diagnostics required.
>>
>> Function parameters could be changed if it was passed by value, and of
>> course, you don't call any unpure functions.
>> Example:
>> [[pure]] std::string AddX(std::string str)
>> {
>> str.append("X");
>> return str;
>> }
>>
>> Is fine.
>>
>> Yes, the compiler might assume that the function produces the same effect
>> for the same arguments. It is up to the implementation, but generally you
>> could make a lookup table or just call the function one and store its
>> result.
>>
>> Tymi.
>>
>> On Tue, 4 Mar 2025, 08:07 Tymi, <tymi.cpp_at_[hidden]> wrote:
>>
>>> Some functions have no side effects, and while they can be often
>>> optimised, the compiler is not aware of that.
>>> Consider this example:
>>> ```cpp
>>> template <std::arithmetic T> constexpr T(const T a, const T b) { return
>>> a + b; }
>>> ```
>>> That function could be declared as pure, or in other words, produces no
>>> side effects.
>>>
>>> I think this is a great way to optimise frequent calls, such as a pure
>>> function's result can be cached for the same arguments provided.
>>>
>>> Diagnostics: if a pure function has side effects, the compiler shall
>>> issue a warning and calling that function is undefined.
>>>
>>> pure member function shall be declared as const, otherwise, the program
>>> is ill-formed.
>>>
>>> --
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