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Okay, so I can't duplicate the exact OO syntax issues I was having before. But, from memory, I was finding that by putting the wrong kind of statement between t

Okay, so I can't duplicate the exact OO syntax issues I was having before. But, from memory, I was finding that by putting the wrong kind of statement between the type definition and the method declaration, I could thoroughly upset the compiler --- there was invisible syntax connecting the two together, and if you I put the wrong thing in between, then things stopped working. But as I can't duplicate it it's entirely possible I was just hallucinating. In general I find the OO syntax desperately confusing. It feels like it's been shoehorned in on top of the existing record and procedure syntax, and it's never clear exactly what anything does. e.g. you need to suffix the object type with 'class in methods in order to make them non dispatching, but you need to suffix the object type with 'class in variable types if you want them to dynamically dispatch? That's not a happy choice. (Case in point: I've just spent 20 minutes trying to refresh my memory by making this code snippet work. And failing. What am I doing wrong? http://ideone.com/6iPdYF http://ideone.com/6iPdYF) Incidentally, re getadanow.com: that's really nice! And it's not pointing at the Adacore compilers, either; beware of these, as their standard library is GPL, not LGPL, which means you can't distribute binaries built with them. (The standard GNAT version is fine.)

msbarnett 11y ago
> But as I can't duplicate it it's entirely possible I was just hallucinating. There's a thing where if you declare a type A, and then a derived type B, methods on A have to be declared before type B gets declared, because B's declaration "freezes" A. I think it's mostly a single-pass optimization that might have made sense 20 years ago but is meaningless in an era of gigabytes of RAM. > (Case in point: I've just spent 20 minutes trying to refresh my memory by making this code snippet work. And failing. What am I doing wrong? http://ideone.com/6iPdYF http://ideone.com/6iPdYF) The specific error message is: you declared a package, which is basically a header in C parlance. You declare signatures in it, not method bodies. Method bodies go in package bodies. You were conflating the package and the package body. And then from line 19 onwards you were using the package name where you wanted to be using a class name. I cleaned it up a bit and made it work: https://gist.github.com/mbarnett/9c6701fe74524a6df522 https://gist.github.com/mbarnett/9c6701fe74524a6df522
- david-given 11y ago
  > There's a thing where if you declare a type A, and then a derived type B, methods on A have to be declared before type B gets declared... Yes, that sounds very familiar. > The specific error message is: you declared a package, which is basically a header in C parlance. Oh, FFS. That snippet is not, in fact, pointing at the piece of code I was actually asking about --- ideone changed it when I wasn't looking. The one you saw is unfinished and broken. This one is the one I was meaning: http://ideone.com/skZRIb http://ideone.com/skZRIb The .Foo selector isn't found; changing it to Foo(object) reports that apparently Foo isn't a dispatching method on MyClass1... which makes no sense, because this is the same code as you had. My suspicion is that there's something magic about declaring classes in packages?
  - msbarnett 11y ago
    > which makes no sense, because this is the same code as you had. My suspicion is that there's something magic about declaring classes in packages? Yeah. Dispatching methods on a type consist of the type's "primitive operations". The Ada 95 Rationale spells it out: "Just as in Ada 83, derived types inherit the operations which "belong" to the parent type - these are called primitive operations in Ada 95. User-written subprograms are classed as primitive operations if they are declared in the same package specification as the type and have the type as parameter or result." It seems like a wart that you're not in an "anonymous" package in situations like your example, but I also guess it probably doesn't come up much in "real" programs.

msbarnett 11y ago

> But as I can't duplicate it it's entirely possible I was just hallucinating. There's a thing where if you declare a type A, and then a derived type B, methods on A have to be declared before type B gets declared, because B's declaration "freezes" A. I think it's mostly a single-pass optimization that might have made sense 20 years ago but is meaningless in an era of gigabytes of RAM. > (Case in point: I've just spent 20 minutes trying to refresh my memory by making this code snippet work. And failing. What am I doing wrong? http://ideone.com/6iPdYF http://ideone.com/6iPdYF) The specific error message is: you declared a package, which is basically a header in C parlance. You declare signatures in it, not method bodies. Method bodies go in package bodies. You were conflating the package and the package body. And then from line 19 onwards you were using the package name where you wanted to be using a class name. I cleaned it up a bit and made it work: https://gist.github.com/mbarnett/9c6701fe74524a6df522 https://gist.github.com/mbarnett/9c6701fe74524a6df522

david-given 11y ago
> There's a thing where if you declare a type A, and then a derived type B, methods on A have to be declared before type B gets declared... Yes, that sounds very familiar. > The specific error message is: you declared a package, which is basically a header in C parlance. Oh, FFS. That snippet is not, in fact, pointing at the piece of code I was actually asking about --- ideone changed it when I wasn't looking. The one you saw is unfinished and broken. This one is the one I was meaning: http://ideone.com/skZRIb http://ideone.com/skZRIb The .Foo selector isn't found; changing it to Foo(object) reports that apparently Foo isn't a dispatching method on MyClass1... which makes no sense, because this is the same code as you had. My suspicion is that there's something magic about declaring classes in packages?
- msbarnett 11y ago
  > which makes no sense, because this is the same code as you had. My suspicion is that there's something magic about declaring classes in packages? Yeah. Dispatching methods on a type consist of the type's "primitive operations". The Ada 95 Rationale spells it out: "Just as in Ada 83, derived types inherit the operations which "belong" to the parent type - these are called primitive operations in Ada 95. User-written subprograms are classed as primitive operations if they are declared in the same package specification as the type and have the type as parameter or result." It seems like a wart that you're not in an "anonymous" package in situations like your example, but I also guess it probably doesn't come up much in "real" programs.