http://d.puremagic.com/issues/show_bug.cgi?id=7176

           Summary: Lambda => syntax for function and methods too
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2011-12-28 05:11:07 PST ---
(From an idea of Timon Gehr)

I think extending the applicability of the new lambda syntax to free functions/methods is a nice idea, to shorten tiny functions/methods, that are common enough:


struct C {
    int x;
    int getX() => x;
    int sqrX() => x ^^ 2;
}


Some examples from other languages:

A function to compute the arithmetic mean in Scala 2.7:

def mean(s: Seq[Int]) = s.foldLeft(0)(_+_) / s.size


From the Ada 2012 changes: http://www.disca.upv.es/jorge/ae2010/slides/05-3_Language_Tech_Schonberg_Towards_Ada_2012.pdf

> To simplify the writing of pre/postconditions and predicates, allow parametrized expressions (aka function bodies in package specs):

function Cube (X : integer) is (X ** 3);

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--- Comment #1 from bearophile_hugs@eml.cc 2012-01-03 16:07:57 PST ---
There are 3 votes now. But this feature doesn't add a lot to D. This feature looks nice, but I don't feel a need for it in my code.

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Jonathan M Davis <jmdavisProg@gmx.com> changed:

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--- Comment #2 from Jonathan M Davis <jmdavisProg@gmx.com> 2012-01-03 16:28:36 PST ---
It would be too much of a departure from the normal syntax to enable the new lambda syntax in general IMHO. It's useful for lambdas simply because without it they risk being very verbose in what is already fairly dense code. Function declarations don't really have that problem. Yes, the syntax is a bit verbose if all you're doing is returning a value, but most functions do more than that, and most functions are not declared in the midst of dense code like you typically get with lambdas. This enhancement request is such a drastic departure from the normal C-based syntax that I think that it would cause far more harm than good.

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timon.gehr@gmx.ch changed:

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--- Comment #3 from timon.gehr@gmx.ch 2012-01-03 16:40:47 PST ---
It is the same 'departure' as the one caused by the introduction of the new lambda literals and therefore I cannot see how it can possibly cause any harm.

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--- Comment #4 from Jonathan M Davis <jmdavisProg@gmx.com> 2012-01-03 16:48:12 PST ---
It's very different IMHO to introduce it in lambdas which are already part of an expression and where the number of characters definitely matters than it is to introduce it in normal function declarations. With declarations, they're on their own instead of part of a larger expression. They just don't present the same kind of gain and therefore don't merit the cost of the large departure in syntax IMHO.

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--- Comment #5 from bearophile_hugs@eml.cc 2012-01-03 16:54:10 PST ---
(In reply to comment #2)

Currently I am neutral toward this feature. I see it used in Scala and it looks nice, but I don't think it will improve my D programs a lot.


> This enhancement request is such a drastic
> departure from the normal C-based syntax that I think that it would cause far
> more harm than good.

What kind of harm are you referring to?

I think it's not significantly bug-prone, and being already present in the language (as lambda syntax) doesn't add a lot of complexity for the person that has to learn D.

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--- Comment #6 from Jonathan M Davis <jmdavisProg@gmx.com> 2012-01-03 19:10:35 PST ---
> What kind of harm are you referring to?

It doesn't fit with the rest of the language. The syntax is very different from other declarations. This reduces readability and increases how much the programmer has to deal with.

The verboseness of lambda expressions is a definite problem for readability, so the syntax is arguably worth it for lambda expressions. But to then also use it in declarations which don't have the same readibility problem is incurring that cost where it's not worth it IMHO.

Obviously, this is perfectly valid as an enhancement request, but I hope that the request is denied. I think that the lambda syntax is too different from typical C-based syntax to be reasonable in normal function declarations.

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Jacob Carlborg <doob@me.com> changed:

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--- Comment #7 from Jacob Carlborg <doob@me.com> 2012-01-03 23:30:48 PST ---
I could really have a use for this. I have a lot of methods that just returns a single expression.

Another idea would be to allow optional braces for methods and functions, just as for if-statements. This could be extended to all language features where braces are used to make it more consistent.

In addition to the above we could make implicit returns possible to all functions and methods.

I don't know which of these two ideas are farthest away from the normal C-based syntax.

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David Piepgrass <qwertie256@gmail.com> changed:

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--- Comment #8 from David Piepgrass <qwertie256@gmail.com> 2012-07-18 17:45:27 PDT ---
+1 from me. Limited C compatibility is one thing, but why should everything in D look like C? Although I've written more code in C/C++ than any other language, I haven't enjoyed it for many years now. I want a language that makes me more productive, and I often use small functions (many of which return void regardless of the expression type, btw, so that should be allowed.)

On the other hand, a lot of the small functions I write are boilerplate such as property getters and forwarding functions in decorators, so maybe instead of a special lambda syntax, what I really want is a few metaprograms to write those functions for me.

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--- Comment #9 from Jacob Carlborg <doob@me.com> 2012-07-18 23:20:18 PDT ---
(In reply to comment #8)

> On the other hand, a lot of the small functions I write are boilerplate such as property getters and forwarding functions in decorators, so maybe instead of a special lambda syntax, what I really want is a few metaprograms to write those functions for me.

I wouldn't mind some kind of property shortcut, like this:

class Foo
{
    @property int bar;
}

Is lowered to this:

class Foo
{
    private int bar_;

    @property int bar () { return bar_; }
    @property int bar (int value) { return bar_ = value; }
}

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