Function attribute best practices

[Paul Backus]

On Tuesday, 13 September 2022 at 14:16:39 UTC, Ali Çehreli wrote:
> On 9/12/22 09:39, Paul Backus wrote:
>
> > Yes. Except for `@trusted`, explicit attributes on template
> code are a
> > smell.
>
> Except for 'const' as well because some templates are member 
> functions. And 'const' on a member function cannot be left to 
> inference because it happens to be a part of the type of the 
> function, which can be overloaded.

Yes, good point. In my head, I think of attributes that apply to 
the `this` parameter like `const`, `inout`, `shared`, and so as 
being in a separate category from attributes that apply to the 
function itself, like `@safe` and `@trusted`.

> Somebody needs to create a two dimensional table that shows 
> what it means for each function attribute on a regular 
> function, member function, and templates of those, and 
> hopefully come up with some guidelines.

Here's my attempt, covering all the attributes found under 
[`MemberFunctionAttribute`][1] in the language spec:

|Attribute|Affects |Inferred?|
|---------|--------|---------|
|nothrow  |Function|Yes      |
|pure     |Function|Yes      |
|@nogc    |Function|Yes      |
|@safe    |Function|Yes      |
|@system  |Function|Yes      |
|@trusted |Function|No       |
|@property|Function|No       |
|@disable |Function|No       |
|const    |this    |No       |
|immutable|this    |No       |
|inout    |this    |No       |
|shared   |this    |No       |
|return   |this    |Yes      |
|scope    |this    |Yes      |

In general, attributes with a 'Yes' in the 'Inferred?' column 
should not be applied explicitly to functions that are subject to 
[attribute inference][2]. This includes functions defined inside 
templates, as well as nested functions and functions with an 
inferred return type (i.e., `auto` functions).

[1]: https://dlang.org/spec/function.html#MemberFunctionAttributes
[2]: 
https://dlang.org/spec/function.html#function-attribute-inference