Bug 12411 – New eponymous template syntax could support nested eponymous templates

Example code: ----- import std.typetuple; enum canAppend(R) = anySatisfy!(canAppendRange!R, Types); private alias Types = TypeTuple!(int, float); // problem: can't use new-style eponymous syntax for nexted templates private template canAppendRange(R) { enum canAppendRange(T) = is(typeof({ R r = void; T t = void; r ~= t; })); } void main() { static assert(canAppend!(int[])); static assert(canAppend!(float[])); static assert(!canAppend!(byte[])); } ----- Notice how 'canAppendRange' has to use the old-style eponymous syntax in order for it to be usable with partial instantiation in the call to anySatisfy. Perhaps a somewhat reasonable enhancement would be to allow nested eponymous syntax: ----- enum canAppendRange(R)(T) = is(typeof({ R r = void; T t = void; r ~= t; })); ----- A simplified example test-case: ----- // old-style template isEqual(T1) { template isEqual(T2) { enum bool isEqual = is(T1 == T2); } } // new-style enum isEqual(T1)(T2) = is(T1 == T2); void main() { alias isInt = isEqual!int; static assert(isInt!int); } ----- The whole idea is to allow new syntax to allow easier writing of templates which can be partially instantiated.

Can just use this now: ----- enum isEqual(T1, T2) = is(T1 == T2); void main() { alias isInt = isEqual!int; static assert(isInt!int); } ----- It works fine.