31 lines
1.7 KiB
Plaintext
31 lines
1.7 KiB
Plaintext
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[[modules-scripting-painless-dispatch]]
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=== How painless dispatches functions
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Painless uses receiver, name, and https://en.wikipedia.org/wiki/Arity[arity]
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for method dispatch. For example, `s.foo(a, b)` is resolved by first getting
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the class of `s` and then looking up the method `foo` with two parameters. This
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is different from Groovy which uses the
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https://en.wikipedia.org/wiki/Multiple_dispatch[runtime types] of the
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parameters and Java which uses the compile time types of the parameters.
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The consequence of this that Painless doesn't support overloaded methods like
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Java, leading to some trouble when it whitelists classes from the Java
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standard library. For example, in Java and Groovy, `Matcher` has two methods:
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`group(int)` and `group(String)`. Painless can't whitelist both of these methods
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because they have the same name and the same number of parameters. So instead it
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has `group(int)` and `namedGroup(String)`.
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We have a few justifications for this different way of dispatching methods:
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1. It makes operating on `def` types simpler and, presumably, faster. Using
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receiver, name, and arity means that when Painless sees a call on a `def` object it
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can dispatch the appropriate method without having to do expensive comparisons
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of the types of the parameters. The same is true for invocations with `def`
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typed parameters.
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2. It keeps things consistent. It would be genuinely weird for Painless to
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behave like Groovy if any `def` typed parameters were involved and Java
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otherwise. It'd be slow for it to behave like Groovy all the time.
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3. It keeps Painless maintainable. Adding the Java or Groovy like method
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dispatch *feels* like it'd add a ton of complexity which'd make maintenance and
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other improvements much more difficult.
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