gcc/testsuite/gdc.test/compilable/test23174.d

   1 // https://issues.dlang.org/show_bug.cgi?id=23174
   2
   3 alias AliasSeq(T...) = T;
   4
   5 template staticMap(alias fun, args...)
   6 {
   7     alias staticMap = AliasSeq!();
   8     static foreach(arg; args)
   9         staticMap = AliasSeq!(staticMap, fun!arg);
  10 }
  11
  12 template Filter(alias pred, args...)
  13 {
  14     alias Filter = AliasSeq!();
  15     static foreach (arg; args)
  16         static if (pred!arg)
  17             Filter = AliasSeq!(Filter, arg);
  18 }
  19
  20 struct Fields(T)
  21 {
  22     private static alias toField(alias e) = Field!(__traits(identifier, e));
  23     alias fields = staticMap!(toField, T.tupleof);
  24
  25     static alias map(alias F) = staticMap!(F, fields);
  26     static alias filter(alias pred) = Filter!(pred, fields);
  27 }
  28
  29 struct Field(string n)
  30 {
  31     enum name = n;
  32 }
  33
  34 struct Foo
  35 {
  36     int a;
  37 }
  38
  39 void test23174()
  40 {
  41     Foo value;
  42
  43     enum toName(alias e) = e.name;
  44     enum pred(alias e) = true;
  45
  46     alias a = Fields!(Foo).filter!(pred); // works
  47     static assert(is(a == AliasSeq!(Field!"a")));
  48
  49     alias b = Fields!(Foo).map!(toName); // works
  50     static assert(b == AliasSeq!("a"));
  51
  52     alias c = Fields!(Foo).init.filter!(pred); // works
  53     static assert(is(c == AliasSeq!(Field!"a")));
  54
  55     // OK <- Error: alias `d` cannot alias an expression `Fields().tuple("a")`
  56     alias d = Fields!(Foo).init.map!(toName);
  57     static assert(d == AliasSeq!("a"));
  58 }