rhaj/_archive/rhai_engine/rhaibook/rust/overloading.md

Function Overloading

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Functions registered with the [Engine] can be overloaded as long as the signature is unique, i.e. different functions can have the same name as long as their parameters are of different numbers (i.e. arity) or different types.

New definitions overwrite previous definitions of the same name, same arity and same parameter types.

Rhai does not support default values for function parameters.

However it is extremely easy to _simulate_ default parameter values via multiple overloaded
registrations of the same function name.

```rust
// The following definition of 'foo' is equivalent to the pseudo-code:
//   fn foo(x = 42_i64, y = "hello", z = true) -> i64 { ... }

fn foo3(x: i64, y: &str, z: bool) -> i64 { ... }
fn foo2(x: i64, y: &str) -> i64 { foo3(x, y, true) }
fn foo1(x: i64) -> i64 { foo2(x, "hello") }
fn foo0() -> i64 { foo1(42) }

engine.register_fn("foo", foo0)     // no parameters
      .register_fn("foo", foo1)     // 1 parameter
      .register_fn("foo", foo2)     // 2 parameters
      .register_fn("foo", foo3);    // 3 parameters
```