You have 'str.append("...")' in your example. Is that really 'pure' as it
would need to allocate memory? In the "virtual C++"-machine that may be
considered "pure" but from a real physical machine it is anything but pure.

// Robin

On Tue, Mar 4, 2025, 12:45 Tymi via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> In your second example, the arguments are the same if:
> 1. Arguments are constexpr and implement a constexpr operator==
> 2. Are trivial and their byte layout is known at compile time
> 3. Exceptions for standard containers that can but don't have to make them
> the same, implementation defined.
>
> On Tue, 4 Mar 2025, 12:43 Tymi, <tymi.cpp_at_[hidden]> wrote:
>
>> Hi Ell,
>>
>> Well, if the function arguments change (as in your 1st example), then
>> they are not the same.
>> In your second example, it could be implementation defined, so, I don't
>> know.
>>
>> 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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