• d-bugmail puremagic.com (40/40) Feb 28 2019 https://issues.dlang.org/show_bug.cgi?id=19708

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=19708

          Issue ID: 19708
           Summary: Can't use __traits(getAttributes, ...)[...] as a type
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: moonlightsentinel disroot.org

The result of __traits(getAttributes, ...)[..] can't be used as a type. Instead
dmd produces some misleading error messages depending on the context.

Consider the following example:

---------------

module test;

struct Foo {}
 Foo int bar;

alias TR = __traits(getAttributes, bar);

/* Error: TR[0] is not a type
TR[0] a;
*/

/* Error: type Foo is not an expression
typeof(TR[0]) b;
*/

/* alias `test.c` cannot alias an expression Foo
alias c = TR[0];
*/

/* __traits(getAttributes, bar) does not give a valid type
alias d = __traits(getAttributes, bar)[0];
*/

// Possible workaround using a tuple
alias Tuple(T...) = T;
alias TP = Tuple!(__traits(getAttributes, bar));

TP[0] e;

---------------

Probably related to issue 16390

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