Bug 21258 – Tuple parameters with defaults use the first tuple element for all defaults since 2.094.0-beta.1

alias AliasSeq(TList...) = TList; int foo(AliasSeq!(int, int) args = AliasSeq!(3, 5)) { return args[0] * args[1]; } static assert(foo(2) == 10); // fails in 2.094.0-beta.1 static assert(foo() == 15); // fails in 2.094.0-beta.1 This used to give defaults of 3 and 5 but now gives defaults of 3 and 3 as of 2.094.0-beta.1. More generally any tuple parameter with tuple defaults just tries to apply the first default value to all arguments. Looks like it was broken by https://github.com/dlang/dmd/pull/11564

It's even more fun if you try it with different types: alias AliasSeq(TList...) = TList; auto foo(AliasSeq!(int, string) args = AliasSeq!(3, "hello")) { return args[0] * args[1].length; } static assert(foo() == 15); // Error: cannot implicitly convert expression 3 of type int to string

@Geod24 created dlang/dmd pull request #11749 "Fix 21258 - Tuple parameters use the first element of a default tuple value" fixing this issue: - Fix 21258 - Tuple parameters use the first element of a default tuple value A single character sometimes means the world. https://github.com/dlang/dmd/pull/11749

dlang/dmd pull request #11749 "Fix 21258 - Tuple parameters use the first element of a default tuple value" was merged into stable: - 8d3fe8fe5bf12a4bf493ddcd78bc4f6a82118784 by Geod24: Fix 21258 - Tuple parameters use the first element of a default tuple value The logic tried to use a single variable for both keeping track of the original index and the extended index, but actually only tracked the extended index. Since `if (tupleStartIdx < eidx) tupleStartIdx = eidx` would be true for every iteration, we would always assign the value at index 0. https://github.com/dlang/dmd/pull/11749

dlang/dmd pull request #11793 "merge stable" was merged into master: - e0a9304324b7d1d2fcf9662c2f77b5c42e804b05 by Geod24: Fix 21258 - Tuple parameters use the first element of a default tuple value The logic tried to use a single variable for both keeping track of the original index and the extended index, but actually only tracked the extended index. Since `if (tupleStartIdx < eidx) tupleStartIdx = eidx` would be true for every iteration, we would always assign the value at index 0. https://github.com/dlang/dmd/pull/11793