Type tuples can't be sliced with boundaries that involve CTFE-able function call(s). The following valid code doesn't compile (both D1 & D2): -------------------- template T(_...) { alias _ T; } size_t mid(size_t n) { return n/2; } alias T!(int, int, int)[0 .. mid($)] A; // Error: Integer constant expression expected instead of mid(3u) -------------------- Patch against dmd r687, makes it sure that TypeSlice boundaries get CTFE'd. --- src/mtype.c +++ src/mtype.c @@ -7787,11 +7787,11 @@ Type *TypeSlice::semantic(Loc loc, Scope *sc) TypeTuple *tt = (TypeTuple *)tbn; lwr = semanticLength(sc, tbn, lwr); - lwr = lwr->optimize(WANTvalue); + lwr = lwr->optimize(WANTvalue | WANTinterpret); uinteger_t i1 = lwr->toUInteger(); upr = semanticLength(sc, tbn, upr); - upr = upr->optimize(WANTvalue); + upr = upr->optimize(WANTvalue | WANTinterpret); uinteger_t i2 = upr->toUInteger(); if (!(i1 <= i2 && i2 <= tt->arguments->dim))
Created attachment 776 [details] Patch against dmd r687, CTFE on tuple slice boundaries The attached patch obsoletes the patch in comment #0. The new one applies the same fix to other relevant parts, and fixes following additional cases: template T(_...) { alias _ T; } size_t mid(size_t n) { return n/2; } alias T!(int, int)[0 .. mid($)] A; // A alias T!(1, 2, 3)[0 .. mid($)] B; // B void main() { T!(int, int, int) values; auto slice = values[0 .. mid($)]; // C }
http://www.dsource.org/projects/dmd/changeset/696