Coercions

One of Notch's most powerful features is agnosticism against numerical types. Internally it supports every JVM native numeric type plus BigDecimal and BigInteger.

The problem

The JVM does not auto-coerce numeric types at runtime. If you pass an int to a method declared void myMethod(long), you would normally throw an exception.

The Notch solution

Notch lets language designers define a set of coercions used during method estimation and invocation. Coercions live in edu.montana.notch.types.coercions.Coercion.

The runtime walks the registered coercions in priority order. When a candidate method's parameter type does not match the argument type, the runtime checks whether any coercion can bridge the two. If one can, the coercion is applied and the method is invoked.

Built-in coercions

The runtime ships two coercions today, both registered in Coercion.registerDefaultCoercions():

• BoxedToPrimitive - bridges the boxed/primitive pairs Integer and int, Long and long, Boolean and boolean, Double and double.
• BigDecimalToInt - bridges BigDecimal and int.

Numeric widening across distinct types (e.g. int -> long, int -> double) is on the roadmap but does not yet ship as a registered coercion.

Adding a coercion

The Coercion class is intended for extension. Today there is no public registration API - all built-in coercions are added inside the static registerDefaultCoercions() initializer. To add your own you would extend Coercion and register it from inside the runtime. See Extending Chisel for the chisel-side API surface.

See also

• Overview for the basics of JVM method calls.
• Chisel Overview for chisel's role as the foundation under Notch.