Impure vs Pure function example.

impure-vs-pure.cs

class Foo {
	private int _someVariable, _someOtherVariable;

	void Update() {
		DoSomething(); // No way of knowing what this mutates without reading it :(
		// The set variables are only used in the same flow
	  	Log(_someVariable, _someOtherVariable);
	}	

	private void Inner() {
		if(true) InnerInner();
		else {
			// Easy to miss that you're resetting variables here,
			//  what if you're adding another variable later?
			_someVariable = 0;
			_someOtherVariable = 0;
		}
	}

	private void InnerInner() {
		if(true) _someVariable = 1;
		else _someVariable = 2; 

		_someOtherVariable = 3;
	}
}

class Bar {
	void Update() {
		// Nice short, and functional
		var (someVariable, someOtherVariable) = DoSomething();
		Log(someVariable, someOtherVariable);
	}	

	private (int, int) Inner() {
		// A lot less to read
		if(true) return InnerInner();
		return (0, 0);
	}

	private (int, int) InnerInner() {
		int someVariable;
		if(true) someVariable = 1;
		else someVariable = 2; 

		return (someVariable, 3);
	}
}

class Baz {
	void Update() {
		// Works just as well (and can be burst compiled!)
		DoSomething(out var someVariable, out var someOtherVariable);
		Log(someVariable, someOtherVariable);
	}

	private void Inner(out int someVariable, out int someOtherVariable) {
		if(true) {
			InnerInner(out someVariable, out someOtherVariable);
			return
		};
		// Being able to see what's assigned to what is a plus!
		someVariable = 0;
		someOtherVariable = 0;
	}

	private (int, int) InnerInner(out int someVariable, out int someOtherVariable) {
		if(true) someVariable = 1;
		else someVariable = 2; 

		someOtherVariable = 3;
	}
}