On Monday, 27 August 2018 at 09:50:01 UTC, Andrey wrote:
alias Pair(alias key, alias value) = AliasSeq!(key, value);
alias Pairs = AliasSeq!(Pair!(Option.First,
handler!(Option.First)), Pair!(Option.Second,
handler!(Option.Second)), handler);
You can't nest AliasSeqs. If you examine Pairs with pragma(msg,
...), you'll see that the inner AliasSeqs have been expanded, and
their members inserted into the outer sequence. As a result, when
you attempt to iterate over the pairs later, you're actually
iterating over the individual Options and handlers, one at a time:
static foreach(pair; pairs)
{
case pair.key:
pair.value(args, i);
break;
}
Also, you can't use the dot operator to access parameters of a
template like that.
onlineapp.d(52): Error: template instance `parseArgs!("-first",
handler, "-second", handler, handler)` does not match template
declaration parseArgs(alias sequence)(ushort index, string[]
args)
Here again, your AliasSeq "Pairs" is being expanded into multiple
template arguments, rather than being passed as a single one. If
you want to pass an AliasSeq to a template, you have to use a
variadic template.
Further reading:
https://dlang.org/spec/template.html#variadic-templates
https://dlang.org/articles/ctarguments.html
