https://issues.dlang.org/show_bug.cgi?id=19127

| <dhasenan@gmail.com> changed:

           What    |Removed                     |Added
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           Keywords|                            |accepts-invalid, spec

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https://issues.dlang.org/show_bug.cgi?id=19127

Seb <greensunny12@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |greensunny12@gmail.com
           Hardware|x86_64                      |All
                 OS|Linux                       |All

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https://issues.dlang.org/show_bug.cgi?id=19127

--- Comment #1 from | <dhasenan@gmail.com> ---
Other things you can use as UDAs:

* modules: @(std.stdio)
* packages: @(std)
* references to members: struct A { int i; } @(A.i)
* uint s; @(s++). This UDA changes every time you access it.
* @(new Object). Likewise.
* string str; @(str ~= "x"). Likewise.

The only thing that doesn't work is declarations, because that's forbidden by the grammar. It seems like there's no special semantic analysis applied other than recursing into child expressions.

Lowering should help:

@Something int x;

into

immutable __tmp = Something;
@__tmp int x;

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https://issues.dlang.org/show_bug.cgi?id=19127

--- Comment #2 from | <dhasenan@gmail.com> ---
Correction: non-CTFEable expressions besides function calls without arguments cannot be used as UDAs. Some of my testing was incorrect. Had B4S1L3 on IRC been more professional or friendly, I might have seen that sooner.

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https://issues.dlang.org/show_bug.cgi?id=19127

--- Comment #3 from | <dhasenan@gmail.com> ---
Oh hey, more fun:

---
module test2;
import std.stdio;
struct S
{
    this(int i) { writeln(i); }
}
size_t print(string s = "hello world")
{
    writeln(s);
    return s.length;
}
size_t x(size_t i) { return i + 1; }
struct A { static uint x; }
string s = "";
int i;

@(std.stdio)
@(new Object)
@(x(4))
@(S(1))
@(A.x)
@(A.x++)
@print
int j;
pragma(msg, __traits(getAttributes, j).stringof);
---

With the pragma(msg), this compiles. Without, it doesn't. Weee!

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https://issues.dlang.org/show_bug.cgi?id=19127

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
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           Priority|P1                          |P2

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https://issues.dlang.org/show_bug.cgi?id=19127

Nick Treleaven <nick@geany.org> changed:

           What    |Removed                     |Added
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                 CC|                            |nick@geany.org

--- Comment #4 from Nick Treleaven <nick@geany.org> ---
> "User-Defined Attributes (UDA) are compile-time expressions that can be attached to a declaration."

Fixed this wording in https://github.com/dlang/dlang.org/pull/3598.

> This should be invalid:

>  struct jsonize { string name; }
>  @jsonize int i;

> `jsonize` is a type, but it is used as an expression. We see how this misbehaves when we inspect it:

>  foreach (uda; __traits(getAttributes, i)) writeln(uda);
>  // Error: cannot pass type jsonize as a function argument

It is actually correct, a UDA can be defined by a type name. And naturally you can't pass a type as a function argument. You can use it in declarations, scroll down to the getAttributes example: https://dlang.org/spec/attribute.html#uda

The other behaviour is very weird for @print. Also non-compile-time expressions should definitely be disallowed.

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https://issues.dlang.org/show_bug.cgi?id=19127

Basile-z <b2.temp@gmx.com> changed:

           What    |Removed                     |Added
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                 CC|                            |b2.temp@gmx.com

--- Comment #5 from Basile-z <b2.temp@gmx.com> ---
The specs have changed since. Neia, can you re-evluate the validity of your report  ?

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