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Version 2 (modified by Chuck, 9 years ago)

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Mixins

Compared to Extensions

  • Extensions enable adding methods to existing classes whereas mixins only augment types that you declare.
  • Mixins can add state (object variables declared with var) whereas extensions cannot.
  • Mixins can add properties whereas extensions cannot.
  • Mixin members will be found at run-time via reflection whereas extension members will not.

In summary, mixins are more about multiple inheritance among the types you are declaring. Extensions are about adding convenience methods to existing types (regardless of who declared them).

Restrictions

As we gain more experience with using mixins, and as the implementation of mixins matures, some of the following restrictions are likely to be removed:

  • Mixins cannot inherit from other types.
  • Mixins cannot implement interfaces.
  • Mixins cannod add other mixins.
  • Mixins cannot declare generic parameters.
  • Mixins cannot add invariants.
  • Two or more mixins added to a single type cannot have collision in their member names.

See also