On Saturday, 26 December 2015 at 19:38:16 UTC, Fusxfaranto wrote:
On Saturday, 26 December 2015 at 19:30:24 UTC, karthikeyan
wrote:
How to instantiate a map with multiple functions. I looked
into the docs at
http://dlang.org/phobos/std_algorithm_iteration.html#map. They
contain a string which I suppose is a mixin and when I change
"a" to some other name it results in an error for me. Are
there any ways to use lambda functions directly instead of
strings and any explanation of the strings used in the map
example and why a is used will be helpful.
I tried reading the source
https://github.com/D-Programming-Language/phobos/blob/master/std/algorithm/iteration.d#L520 .Some hint that "a" should be used at https://github.com/D-Programming-Language/phobos/blob/master/std/functional.d#L101 but how do I change that since map doesn't allow me any params to specify the parameter name. Also how can I map an array of tuples with two or more elements with a function of two or more params like unpack the tuple into a function like that. I am D beginner so any will insights will be very helpful for me.
I am using dmd version 2.069 on Linux Mint 15 - 64bit
You should be able to just use any function (including lambdas)
as a template argument to map. The string version is from
before the more concise "=>" lambda syntax was developed, and
generally isn't what you want to use nowadays.
Thanks but the following returns an error for me
import std.algorithm.comparison : equal;
import std.range : chain;
int[] arr1 = [ 1, 2, 3, 4 ];
int[] arr2 = [ 5, 6 ];
auto dd = map!(z => z * z, c => c * c * c)(chain(arr1, arr2));
writeln(dd);
Error :
/usr/include/dmd/phobos/std/meta.d(546): Error: template instance
F!(__lambda2) cannot use local '__lambda2' as parameter to
non-global template AppliedReturnType(alias f)
/usr/include/dmd/phobos/std/meta.d(552): Error: template instance
maps_square.main.staticMap!(AppliedReturnType, __lambda2) error
instantiating
/usr/include/dmd/phobos/std/algorithm/iteration.d(447):
instantiated from here: staticMap!(AppliedReturnType, __lambda2,
__lambda3)
maps_square.d(71): instantiated from here: map!(Result)
/usr/include/dmd/phobos/std/meta.d(546): Error: template instance
F!(__lambda3) cannot use local '__lambda3' as parameter to
non-global template AppliedReturnType(alias f)
/usr/include/dmd/phobos/std/meta.d(553): Error: template instance
maps_square.main.staticMap!(AppliedReturnType, __lambda3) error
instantiating
/usr/include/dmd/phobos/std/algorithm/iteration.d(447):
instantiated from here: staticMap!(AppliedReturnType, __lambda2,
__lambda3)
maps_square.d(71): instantiated from here: map!(Result)
Am I missing something here over how the lambda notation can be
used? I personally prefer the lambda notation to be clear than
passing strings as arguments. Kindly help me on this.
