How can I have a cyclic dependency in dao?

Label: ♦english ♦miscellaneous

[569] How can I have a cyclic dependency in dao?

Comment

Pompei2 created at Sunday, 2011-01-30, 13:45:42

4 Replies, 1243 Hits

Hello,

I have the following kind of code:

ComponentManager.dao:

load Component;

class ComponentManager {
private
var _components : map<string, map<int, Component>>
}

Component.dao:

load ComponentManager;

interface Component {
sub observe(mgr : ComponentManager)
sub act(mgr : ComponentManager)
}

You can see the cyclic dependency: ComponentManager holds a list of Components, while the Components should have a callback that gets the ComponentManager as parameter.
Unfortunately, this code won't compile (in World.dao, I do "load ComponentManager;"), because when dao gets to Component.dao, it doesn't know the type "ComponentManager" yet:

[[ERROR]] in file "/windows/Xchange/projects/component-system-prototype-fail1/CompSys/Component.dao":
At line 7 : Invalid parameter list for --- " observe ";
[[ERROR]] in file "/windows/Xchange/projects/component-system-prototype-fail1/CompSys/Component.dao":
At line 40 : Invalid interface definition --- " interface Component { routine observe ... ";
[[ERROR]] in file "/windows/Xchange/projects/component-system-prototype-fail1/CompSys/ComponentManager.dao":
At line 3 : loading failed;
[[ERROR]] in file "/windows/Xchange/projects/component-system-prototype-fail1/World.dao":
At line 3 : loading failed;
[[ERROR]] in file "/windows/Xchange/projects/component-system-prototype-fail1/main.dao":
At line 3 : loading failed;

My question is, how could I possibly solve that? And in a more general way, how to work around such a cyclic dependency in dao? Is there something like forward declaration in dao? Or maybe you have a suggestion to restructure my code?

Comments

[570⇒569] ...

Comment

Nightwalker commented at Sunday, 2011-01-30, 14:59:12

Nightwalker modified at Sunday, 2011-01-30, 15:31:42

I encountered similar situation too. You can just define additional interface for ComponentManager in Component.dao ; use it as parameter type for Component 's methods, and then bind that interface to the actual class in ComponentManager.dao . Then you don't need to load ComponentManager.dao in Component.dao , and cross-dependency is eliminated :) However, the interface for ComponentManager will still be unable to explicitly refer to the interface Component (untyped arguments are needed for that instead).

[571⇒569] forward declaration

Comment

fu commented at Sunday, 2011-01-30, 22:06:07

is now supported for both class and interface:)

[572⇒571] ...

Comment

Pompei2 commented at Sunday, 2011-01-30, 22:10:18

Pompei2 modified at Sunday, 2011-01-30, 22:13:12

Wow cool, thanks a bunch!
Edit: I see in the example files, that now you declared the routine inside the class but defined it outside the class (C++-style), was that supported since ever, or did you just add that?

[573⇒572] ...

Comment

fu commented at Tuesday, 2011-02-01, 01:58:18

Define methods outside of class body has been supported for quite sometime:)

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