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digitalmars.D.learn - newbie question: Can D do this?

reply clk <clk clksoft.com> writes:
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Hello,
I'm new to this mailing list.  I'm trying to learn D  to eventually use 
it in production code.
I'm a little bit intimidated by the fact that the topics in the d-learn 
list look rather advanced to a newbie like me.
I have 3 fairly simple questions:

1) Does D support something like the javascript 1.8 destructuring 
assigment (multiple assigment in python):

[a, b] = [b, a];

2) D doesn't  seem to support the list comprehension syntax available in 
python and javascript.  Is this correct?

[f(x) for x in list if condition]

3) D's slice operator apparently doesn't allow the use of a stride other 
than unity as is allowed with fortran and matlab.  Is there a way to 
implement this feature so that

[1, 2, 3, 4, 5][0..$:2] would refer to [1, 3, 5], etc..., where 2 is the 
non unit stride.  Or is the find function from std.algorithm the only 
option to achieve the same behavior.

I find the 3 features above extremely convenient in every day coding.
Thanks,
-clk
Dec 19 2011
next sibling parent simendsjo <simendsjo gmail.com> writes:
On 19.12.2011 17:17, clk wrote:
 1) Does D support something like the javascript 1.8 destructuring
 assigment (multiple assigment in python):

 [a, b] = [b, a];

I don't think so, but you can do something like this with templates: void swap(alias a, alias b)() { auto t = a; a = b; b = t; } int a = 1, b = 2; swap!(a, b); assert(a == 2); assert(b == 1);
 2) D doesn't seem to support the list comprehension syntax available in
 python and javascript. Is this correct?

 [f(x) for x in list if condition]

Don't think so. You can use std.algorithm, but it's a bit harder to read: auto arr = [1,2,3,4,5,6]; auto res = array(pipe!(filter!"a>3", map!"a*2")(arr)); assert(res == [8,10,12]); // or auto res2 = array(map!"a*2"(filter!"a>3"(arr))); assert(res2 == [8,10,12]); But I'm a newbie myself.
Dec 19 2011
prev sibling next sibling parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 12/19/2011 08:17 AM, clk wrote:

 I'm a little bit intimidated by the fact that the topics in the d-learn
 list look rather advanced to a newbie like me.

We need more newbie topics here! :)
 1) Does D support something like the javascript 1.8 destructuring
 assigment (multiple assigment in python):

 [a, b] = [b, a];

No multiple assignment like that. But useful approarches exist for most needs, like the swap that simendsjo has shown.
 2) D doesn't seem to support the list comprehension syntax available in
 python and javascript. Is this correct?

 [f(x) for x in list if condition]

List comprehension is not part of the language. import std.algorithm; void f(int x) {} bool condition(int x) { return true; } void main() { auto list = [ 0, 1, 2 ]; map!f(filter!condition(list)); } You can define f and condition within the body of main(). It is possible to use function literals as well: import std.algorithm; void main() { auto list = [ 0, 1, 2 ]; map!((x){ /* ... this is f(x) ...*/ })(filter!((x) { return true; /* ... condition ... */ })(list)); }
 3) D's slice operator apparently doesn't allow the use of a stride other
 than unity as is allowed with fortran and matlab. Is there a way to
 implement this feature so that

 [1, 2, 3, 4, 5][0..$:2] would refer to [1, 3, 5], etc..., where 2 is the
 non unit stride. Or is the find function from std.algorithm the only
 option to achieve the same behavior.

std.range.stride does that: import std.range; // ... stride([1, 2, 3, 4, 5], 2)
 I find the 3 features above extremely convenient in every day coding.
 Thanks,
 -clk

Ali
Dec 19 2011
prev sibling next sibling parent Kai Meyer <kai unixlords.com> writes:
On 12/19/2011 09:17 AM, clk wrote:
 Hello,
 I'm new to this mailing list. I'm trying to learn D to eventually use it
 in production code.
 I'm a little bit intimidated by the fact that the topics in the d-learn
 list look rather advanced to a newbie like me.
 I have 3 fairly simple questions:

 1) Does D support something like the javascript 1.8 destructuring
 assigment (multiple assigment in python):

 [a, b] = [b, a];

I would love multiple assignment like this, but it's tricky. But your usage isn't really multiple assignment as much as it is a swap. What I'd love is something like this: [a, b, c] = [get_a(), get_b(), get_c()]; Or [a, b, c] = [to!(int)(argv[1]), some_other_value, argv[4]);
 2) D doesn't seem to support the list comprehension syntax available in
 python and javascript. Is this correct?

 [f(x) for x in list if condition]

No, D's syntax is very C-ish. I don't expect syntax like this to ever show up (though what you are doing is possible with things like std.algorithm)
 3) D's slice operator apparently doesn't allow the use of a stride other
 than unity as is allowed with fortran and matlab. Is there a way to
 implement this feature so that

 [1, 2, 3, 4, 5][0..$:2] would refer to [1, 3, 5], etc..., where 2 is the
 non unit stride. Or is the find function from std.algorithm the only
 option to achieve the same behavior.

Ya, std.range, like Ali said.
 I find the 3 features above extremely convenient in every day coding.
 Thanks,
 -clk

Dec 19 2011
prev sibling next sibling parent =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Mon, 19 Dec 2011 17:17:43 +0100, clk <clk clksoft.com> wrote:

 Hello,
 I'm new to this mailing list.  I'm trying to learn D  to eventually use
 it in production code.
 I'm a little bit intimidated by the fact that the topics in the d-learn
 list look rather advanced to a newbie like me.
 I have 3 fairly simple questions:

 1) Does D support something like the javascript 1.8 destructuring
 assigment (multiple assigment in python):

 [a, b] = [b, a];

This, or something quite like it, was covered on Saturday in the thread "Alias/Ref Tuples ?". This works (but is hardly as elegant as Python's syntax: import std.typetuple : TypeTuple; import std.typecons : tuple; TypeTuple!(a, b) = tuple(b,a);
Dec 19 2011
prev sibling parent "Jakob Ovrum" <jakobovrum gmail.com> writes:
On Monday, 19 December 2011 at 19:01:10 UTC, Simen Kjærås wrote:
 import std.typetuple : TypeTuple;
 import std.typecons : tuple;

 TypeTuple!(a, b) = tuple(b,a);

There is a pull request implementing multiple variable declarations: https://github.com/D-Programming-Language/dmd/pull/341 However, the right hand side must still be a tuple.
Dec 19 2011