https://issues.dlang.org/show_bug.cgi?id=23666

Bolpat <qs.il.paperinik@gmail.com> changed:

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                 CC|                            |qs.il.paperinik@gmail.com

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https://issues.dlang.org/show_bug.cgi?id=23666

--- Comment #1 from Bolpat <qs.il.paperinik@gmail.com> ---
Generalization:

To be “aptly constrained” means that the constraint is a type of the following
form:
```d
Int delegate ParameterList MemberFunctionAttributes`
```
where `ParameterList` and `MemberFunctionAttributes` [3, 4] are defined in the
D grammar, and Int is `int` with any type constructors (`const`, `inout`,
`shared`) applied to it (they don’t matter anyways), but it shouldn’t fail
because some type inference made it e.g. `const`.

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https://issues.dlang.org/show_bug.cgi?id=23666

Iain Buclaw <ibuclaw@gdcproject.org> changed:

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           Priority|P1                          |P4

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https://issues.dlang.org/show_bug.cgi?id=23666

Nick Treleaven <nick@geany.org> changed:

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                 CC|                            |nick@geany.org

--- Comment #2 from Nick Treleaven <nick@geany.org> ---
You can use `auto opApply` to infer attributes instead of a template.

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https://issues.dlang.org/show_bug.cgi?id=23666

--- Comment #3 from Bolpat <qs.il.paperinik@gmail.com> ---
(In reply to Nick Treleaven from comment #2)
> You can use `auto opApply` to infer attributes instead of a template.

```d
struct S
{
    auto opApply(int delegate(ref int) callback)
    {
        int x;
        return callback(x);
    }
}

void main() @safe
{
    foreach (ref x; S()) {} // Error: `@safe` function `D main` cannot call
`@system` function `S.opApply`
}
```

However, this does (for reasons beyond my understanding):
```d
struct S
{
    int opApplyImpl(DG : int delegate(ref int))(scope DG callback)
    {
        int x;
        return callback(x);
    }
    alias opApply = opApplyImpl!(int delegate(ref int));
}

void main() @safe
{
    foreach (ref x; S()) {}
}
```

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https://issues.dlang.org/show_bug.cgi?id=23666

--- Comment #4 from Nick Treleaven <nick@geany.org> ---
Sorry, yes. This proposal seems workable.

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https://issues.dlang.org/show_bug.cgi?id=23666

Dlang Bot <dlang-bot@dlang.rocks> changed:

           What    |Removed                     |Added
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           Keywords|                            |pull

--- Comment #5 from Dlang Bot <dlang-bot@dlang.rocks> ---
@Bolpat created dlang/dlang.org pull request #3859 "Specify `opApply` as an alias to a function template instance" fixing this issue:

- Fix Bugzilla Issues 23666, 17953, 23116, and 24633

https://github.com/dlang/dlang.org/pull/3859

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