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Request for explanation of an idiomatic D2 construct

I often come accros the following construct that I don't quite grasp in a D2 source code:

alias uint SymbolRef;

struct SymbolTable {
  alias entries this;
  SymbolRef startSymbol;
  Symbol[] entries;
}

What does imply the alias entries this; inside the type definition given that there is already Symbol[] entries;?

Solution

  • Official docs

    In short: alias this construct is D's way of multiple implementation inheritance. In your example struct SymbolTable should behave similarly to Symbol[] with addition of few extra stuff. It can be implicitly converted to Symbol[].

    However, I have often heard that more complex usage of alias this is considered buggy in current compiler implementation, so better be careful here and ready for bug reports ;)

    Related chapter of "The D Programming Language" is "6.13 Multiple Subtyping"