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From OC <>
Subject Re: Named function arguments in Groovy
Date Wed, 23 Nov 2016 20:01:32 GMT

On 23. 11. 2016, at 8:50, Michael Rüegg <> wrote:

> The problem with this approach is that for a user of this DSL, it is not obvious which
parameters are expected and what their names are (beside documenting it, but who is going
to read that ;-)). 

Well, if someone is too sexy to read documentation, serves him right, does it not?

That said, some way of checking argument names would be nice.

> How can I achieve named function arguments with “real" syntax in Groovy? Is there an
alternative to using maps for this?

It does not need to be an alternative to map; just perhaps adding a way to inform the compiler
which names (and types) are allowed and which are not.

I believe you could DIY through ASTTs, but aside of that, far as I can say, there's currently
no way compile-time. Runtime, of course, you can DIY much easier :)

> By the way, I think it is kind of misleading for a beginner that the following compiles

I would rather think it would be highly suspicious if it did not compile, for beginner or
experienced programmer just as well.

> but does not pass the arguments in the intended order:

It does. The order is as declared.

> foo(a="a", c=“c", b=“b") {
>  // a == a, b == c, c==b
> }
> Is this intended behaviour?

Definitely, since it is nothing Groovy-specific: three very plain positional arguments, whose
values happen to be given using expressions. In this case, assignment expressions.

There are two a's (two b's, two c's) -- one outside the method (and that's the one you assign
the value to by the expression); another inside (and it gets the result of the appropriate
expression, positionally).

Possibly you have tested that in a script, which might get confusing for it (sort of) creates
those outside a, b and c for you automatically without you having to declare it. Try it in
a normal class, and you'll see the trick.

All the best,

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