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References provide a way to share data between instances and to define recursive data types that would otherwise be infinitely large.

A List using references

Here is a small example that defines a feature Node that contains a String and an optional tail that is itself a Node or nil.

When trying to compile this, we get an error due to cyclic types: A Node may not contain itself, so the object layout fails.

A solution is to declare Node to be a ref, i.e., any field of type Node will not contain a Node directly, but only refer to a Node. Now the code compiles and runs:

Dynamic Binding


A reference value of a given feature type f can be assigned to a reference field whose type is a reference to f or, recursively, any of features called in f's inherits clause.

Assigning value instances to references


This should automatically create a reference to the instance (if it is immutable and has a lifespan that exceeds that of the reference) or a copy of the instance.

Assigning reference to value fields


It must be decided if this should be allowed at all, my preference is to forbid it since the dynamic binding gets lost and the resulting behavior may be wrong.

null Reference

There is no null-reference in Fuzion, it avoids the billion-dollar mistake similar to F# or Rust by using a choice type with nil representing the absence of a reference.