最新的設計文檔里面對這一塊做了一個解釋。

Why not use the syntax F like C++ and J***a? When parsing code within a function, such as v := F, at the point of seeing the < it's ambiguous whether we are seeing a type instantiation or an expression using the < operator. This is very difficult to resolve without type information. For example, consider a statement like a, b = w < x, y > (z) Withou…。