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1 // REQUIRED_ARGS: -o-
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2 /*
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3 TEST_OUTPUT:
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4 ---
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5 ---
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6 */
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7
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8 mixin template Helpers()
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9 {
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10 static if (is(Flags!Move))
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11 {
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12 Flags!Move flags;
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13 }
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14 else
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15 {
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16 pragma(msg, "X: ", __traits(derivedMembers, Flags!Move));
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17 }
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18 }
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19
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20 template Flags(T)
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21 {
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22 mixin({
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23 int defs = 1;
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24 foreach (name; __traits(derivedMembers, Move))
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25 {
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26 defs++;
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27 }
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28 if (defs)
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29 {
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30 return "struct Flags { bool x; }";
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31 }
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32 else
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33 {
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34 return "";
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35 }
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36 }());
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37 }
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38
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39 struct Move
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40 {
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41 int a;
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42 mixin Helpers!();
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43 }
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44
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45 enum a7815 = Move.init.flags;
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46
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47 /+
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48 This originally was an invalid case:
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49 When the Move struct member is analyzed:
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50 1. mixin Helpers!() is instantiated.
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51 2. In Helpers!(), static if and its condition is(Flags!Move)) evaluated.
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52 3. In Flags!Move, string mixin evaluates and CTFE lambda.
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53 4. __traits(derivedMembers, Move) tries to see the member of Move.
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54 4a. mixin Helpers!() member is analyzed.
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55 4b. `static if (is(Flags!Move))` in Helpers!() is evaluated
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56 4c. The Flags!Move instantiation is already in progress, so it cannot be resolved.
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57 4d. `static if` fails because Flags!Move cannot be determined as a type.
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58 5. __traits(derivedMembers, Move) returns a 1-length tuple("a").
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59 6. The lambda in Flags!Move returns a string "struct Flags {...}", then
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60 Flags!Move is instantiated to a new struct Flags.
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61 7. Finally Move struct does not have flags member, then the `enum a7815`
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62 definition will fail in its initializer.
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63
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64 Now, static if will behave like a string mixin: it is invisible during its own expansion.
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65 +/
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