foam3

Summary

• implements: declares intent to implement an interface or mix in a model, with special handling to avoid property override conflicts by inserting an intermediate axiom map level.

• mixins: directly copies all axioms from another model into the target class as if they were defined locally, without special conflict resolution.

  Key Differences

  | Aspect | implements: | mixins: | |——–|—————|———–| | Purpose | Declare interface implementation or safe mix-ins; can be used for interfaces with or without implementation | Copy all axioms from another model into this class | | Override handling | Inserts a new level in the class’s axiomMap_ so overridden properties see the correct super-property | No special handling; installs axioms directly | | Property installation | Skips installing properties already present on the class | Installs all own axioms unconditionally | | Error handling | Throws if the interface/mixin does not exist | Warns if the mixin does not exist but continues | | isInstance / isSubClass | Adds an axiom named implements_<path>, so X.isInstance(obj) and X.isSubClass(cls) are true | Adds an axiom named mixin_<path>, so X.isInstance(obj) and X.isSubClass(cls) stay false |

  Code Examples

  Using implements:

  foam.CLASS({
  name: 'AbstractDAOAgent',
  implements: [ 'foam.mlang.Expressions' ],
  // ...
  });
  

  Using mixins:

  foam.CLASS({
  name: 'DAOPrompt',
  mixins: [ 'foam.core.reflow.DAOResolverMixin' ],
  // ...
  });
  

  Implementation Details

• Implements.installInClass performs a complex dance: it avoids re-installing existing properties, then creates a new axiom map level to ensure overrides work correctly.
• Mixin.installInClass simply looks up the model and installs all its own axioms directly, warning if missing.

  When to Use Which

• Use implements: when you need interface-like semantics or safe multiple inheritance with proper override handling.
• Use mixins: for straightforward composition of axioms without concern for override edge cases.

  Notes

• Both are axioms in FOAM’s model system.
• implements: can also be used for pure interfaces (methods without implementation), while mixins: always copies all axioms.
• The Implements axiom has higher priority (200) than Mixin (19), affecting installation order. Wiki pages you might want to explore:
• Advanced Features and Extensions (foam-foundation/foam3)

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