The context is actually "I still am fuzzy about the difference between “square brackets,” “braces,” and “parentheses.”".

You said parens indicate a list, so that would mean %hash should be used.

sub g { return  { ... } }
sub h { return  { ... } }

my %hash = (f ? g : h);
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That's wrong wrong wrong.

I took the context to be like how it was used in the OP -- i.e. something like "When declaring and initializing hashes (%) and arrays (@), do I use {}, [], or () to assign the values?".

Elda Taluta; Sarks Sark; Ark Arks

One never uses {} or [] to initialise a hash or array. No need to make stuff up about ().