On 9/12/22 1:08 PM, Ali Çehreli wrote:
On 9/12/22 09:48, H. S. Teoh wrote:
>> @nogc nothrow pure @safe
>> // ...
>> No, it isn't because unless my unittest code is impure, I can't catch
>> my incorrect 'pure' etc. on my member functions.
> Sure you can. The `pure unittest` code obviously must itself be pure
> (otherwise it wouldn't compile). If Foo introduces impure behaviour,
> then the unittest, being pure, wouldn't be allowed to call Foo's impure
> methods, which is what we want. What's the problem?
There was a problem until you and others put me straigth. :)
What I meant was
- if I put 'pure' etc. on my templatized code,
- and then tested with a 'pure' unittest,
I wouldn't know that the gratuitous use of my 'pure' on the member
function was wrong. I would be fooling myself thinking that I smartly
wrote a 'pure' member function and a 'pure' unittest and all worked.
Wrong idea! :)
So you are thinking about this the wrong way I believe.
When you put `pure` on a template function, you are saying "only
instantiations where this function can be pure are allowed".
Essentially, that's *you* telling your *user* "this must be pure!".
If your intent is to *enforce* pure functions only, then that's what you
do. If your intent instead is to ensure that given proper parameters,
the function will be pure, then the answer is to unittest.
I will say, sometimes this gets really annoying. Like if the unittest
fails, you get very little information about *why* it's not working.
i.e. you expect the inference to be pure, but it's not. All you get is
"impure unittest can't call impure function foo(...)". Figuring out the
misinference cause is a chore today. I wish it would be easier.