Some questions

[satsen]

First of all, thank you for this great library. It is so much simpler than ASM and I can actually do things with it.

I have 2 questions, and I hope that you will be able to help me.

How do I obtain a "Variable" (I think it's not the right thing for this use-case, but I did not find an alternative) for a constant/literal value? Say if I have a boolean variable that I want to assign the expression 1L < 4L to, the only way I found is to do mm.var(long.class).set(1L).lt(4L) which generates:

long var2 = 1L;
boolean var3 = var2 < 4L;

but I tried compiling a class with javac and I got the much simpler

boolean var1 = 1L < 4L;

(javac optimizes this but I tried with a more difficult expression, it still did not generate a single-use variable).

And then that var3 is used in a method invocation, so there's 2 redundant variables. I would love to get to know how I could for example do a simple method(1L < 4L) without 2 redundant variables.

How do I perform logical operations? Like, how can I get a var1 && var2 or a var1 || var2 expression? I only found the bitwise options in the API.

If these could be added to the wiki it would be great. Thanks again for the library.

[broneill]

1. You can do mm.var(boolean.class).set(1L < 4L), but that might not be what you really meant. The code that gets generated sometimes has extra variables, but that's an artifact of not exposing the operand stack. When the bytecode gets compiled by the JVM, these extra variables go away. The old (and deprecated) version of Cojen performed liveness analysis to clean things up, but this was slow and yielded no benefit because HotSpot did the same thing anyhow.
2. I added a new section: https://github.com/cojen/Maker/wiki/Coding-patterns#short-circuit-logical-operations

[broneill]

By the way, some work is performed to reduce local variable usage already, but only for simple cases. The lt operation is actually quite complicated, and as a result, the reduction doesn't work. Simpler operations like add do produce instructions that you would expect -- no extra variable is used.

[satsen]

1. Ok then I guess what I was already doing is the right way (the values are obtained from expressions, so I don't evaluate it on compile-time, 1L and 4L were examples)
2. It is pretty confusing, my compiler is going through the AST with a recursive approach, so I work on specific values, which can be embedded quite deep. Not sure how the if statements would work but I'll try to figure it out

[satsen]

Regarding logical operations, the bitwise AND and OR seems to do the same job as logical AND and OR when used with booleans? I could not figure out what to do with labels in my procedure so I guess I could use that instead.

[broneill]

If you have an AST, generating short-circuit logic code using goto statements is typical, and javac does this too. If the Cojen/Maker library supported short-circuit operations directly, it would need do perform a bunch of reverse engineering to reconstruct an AST first.

You can use the bitwise operations with boolean types, but this doesn't perform short-circuit logic, and so it's not a good substitute.

[satsen]

I honestly have no idea what short-circuit logic even is in this context.

After some more tinkering I figured I could create a boolean Variable that is false to begin with, then have ifFalse for both the left-hand argument and right-hand argument (which at the point where a && or || comparison is being handled, have already been turned into boolean Variables or are boolean Objects-in the case of literals) to skip to a label which is right after a variable = true; statement.

Thanks for the help. The decompiled code isn't "pretty", but it gets the work done.

[satsen]

Cojen/Maker is a great library, thanks again for making it. I'll go work on the other parts of my language (method selection-overloads and varargs can be tough, type promotion, etc.).

If you use cryptocurrency, I'd love to send you a tip in the currency of your choice. As a thank you for the library and the help :)

[satsen]

Hey I ran into another issue, I hope you can help me. So I did a lot of things, and now I need to pass a lambda to a method call.

The method I want to call is public static DoubleBinding createDoubleBinding(Callable<Double>, Observable...) (Observable is a class of the toolkit, don't mind that)

I've done all the LambdaMetafactory things, but when I try to invoke this method, it says Unsupported constant type: class [Lorg.cojen.maker.Variable;

I invoke it like this: mm.var(Bindings.class).invoke("createDoubleBinding", function, observables.toArray()) the observables List contains Variables.

---

I suspect that even if I get past this point I will run into other issues, due to this comment that I read in the wiki
// Note: Extra params are needed if lambda implementation method isn't static.
The lambda accesses a local variable (which is made using mm.var), I'm not sure how I would pass my local variable from the current method to the lambda method, and also not sure whether the lambda method should be static or not.

[broneill]

The function param and the observables need to be passed as combined Object array. The varags param doesn't understand that's what you intend and so it sees the function as the first param, and the array of variables as the second param.

[broneill]

...or do you intend for the Observable... param to be varargs? In that case, you need to pass an Observable array.

var observablesVar = mm.new_(Observable[].class, observables.size());
foreach observable {
    observablesVar.aset(i, observable);
}
mm.var(Bindings.class).invoke("createDoubleBinding", function, observablesVar);