On Tuesday, 22 December 2020 at 21:11:12 UTC, Andre Pany wrote:
I am really confused, why is this valid:
void sample(string[string] s = string[string].init){}
while this causes syntax errors?
void sample_invalid1(double[string] s = double[string].init){}
void sample_invalid2(int[int] s = int[int].init){}
Looks like an oddity in the grammar.
`string` is an alias, meaning it's an identifier. And an
identifier is a valid expression to the grammar. So
`string[string]` is parsed as an IndexExpression. Only during
semantic analysis does the compiler figure out that it's actually
a type.
`double` and `int` aren't identifiers. They're keywords. And
they're always types, never expressions. So `int[int]` cannot be
parsed as an IndexExpression. It's parsed as a Type instead. And
for a (grammatical) Type, there is no rule that allows
`Type.Identifier`.
You can work around with parentheses:
(double[string]).init;
(int[int]).init
