WrapOperation

Allows you to wrap a method call or field get/set.

Your handler method receives the targeted instruction's arguments and an Operation representing the operation being wrapped (optionally followed by the enclosing method's parameters). You should return the same type as the wrapped operation does.

Should be used in favour of Redirects when you are wrapping the original operation and not replacing it outright, as unlike Redirects, this chains when used by multiple people.

Handler Methods

Targeted operation	Handler signature
Non-static method call	private ReturnType yourHandlerMethod(OwnerType instance, <arguments of the original call>, Operation<ReturnType> original)
Static method call	private ReturnType yourHandlerMethod(<arguments of the original call>, Operation<ReturnType> original)
Non-static field get	private FieldType yourHandlerMethod(OwnerType instance, Operation<FieldType> original)
Static field get	private FieldType yourHandlerMethod(Operation<FieldType> original)
Non-static field write	private void yourHandlerMethod(OwnerType instance, FieldType newValue, Operation<Void> original)
Static field write	private void yourHandlerMethod(FieldType newValue, Operation<Void> original)

In all of these cases, you can optionally add the enclosing method's parameters to the end, should you require them for additional context.

Example

When targeting code such as the following:

int number = this.expensiveCalculation(flag);

you may wish to wrap the call such that it is bypassed if a setting is enabled.

This could be done like so:

@WrapOperation(
	method = "targetMethod", 
	at = @At(value = "INVOKE", target = "Lsome/package/TargetClass;expensiveCalculation(Z)I")
)
private int bypassExpensiveCalculationIfNecessary(TargetClass instance, boolean flag, Operation<Integer> original) {
	if (YourMod.bypassExpensiveCalculation) {
                return 10;
        } else {
                return original.call(instance, flag);
        }
}

expensiveCalculation would then only be called if you called it yourself via the original.call(...) invocation.

Multiple mods can do this at the same time, and the wrapping will chain. The first to be applied receives an Operation representing the vanilla call, if another is applied it receives an Operation representing the first one's wrapping, etc.

Code Diff

- int number = this.expensiveCalculation(flag);
+ int number = this.bypassExpensiveCalculationIfNecessary(this, flag, args -> {
+         return ((TargetClass) args[0]).expensiveCalculation((Boolean) args[1]);
+ });