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digitalmars.D - Inline Operator from Function.

reply Jonathan Levi <catanscout gmail.com> writes:
I know this was not an intentional feature of d, but it is a cool 
quirk.

If you want to use a function that takes two arguments like a 
infix binary operator (similar to the back ticks in Haskell 
"`fun`") you can but a "." before and a "=" after.

     c = (a .fun= b);

Example of it working (https://run.dlang.io/is/rr7ChO)

     import std.stdio;

     void main() {
         writeln(5 .mul= 2);
     }

     int mul(int a, int b) {
     	return a*b;
     }
Jan 24 2019
parent reply Neia Neutuladh <neia ikeran.org> writes:
On Fri, 25 Jan 2019 03:45:36 +0000, Jonathan Levi wrote:

 I know this was not an intentional feature of d, but it is a cool quirk.
 
 If you want to use a function that takes two arguments like a infix
 binary operator (similar to the back ticks in Haskell "`fun`") you can
 but a "." before and a "=" after.
 
      c = (a .fun= b);


Consider also:

struct Operator(alias fn) if (Parameters!fn.length == 2)
{
    Curry opBinaryRight(string op)(Parameters!fn[0] arg) if (op == "/")
    {
        return Curry(arg);
    }
    struct Curry
    {
        Parameters!fn[0] arg;
        auto opBinaryRight(string op)(Parameters!fn[1] arg2) if (op == "/")
        {
            return fn(arg, arg2);
        }
    }
}

To use it:

alias min = Operator!((a, b) => a < b ? a : b);
writeln(1 /min/ 2);

Credit to FeepingCreature for inventing this 5-10 years ago.
Jan 24 2019
next sibling parent Neia Neutuladh <neia ikeran.org> writes:
On Fri, 25 Jan 2019 03:52:23 +0000, Neia Neutuladh wrote:

 alias min = Operator!((a, b) => a < b ? a : b);


Er, that should obviously be:

enum min = Operator!(...).init;

Or use a static function for the operator overload. It's a land of 
lawlessness here, do whatever you like.
Jan 24 2019
prev sibling next sibling parent reply Mike Parker <aldacron gmail.com> writes:
On Friday, 25 January 2019 at 03:52:23 UTC, Neia Neutuladh wrote:


 Credit to FeepingCreature for inventing this 5-10 years ago.


2007 it seems, assuming FeepingCreature == downs:

https://forum.dlang.org/post/fg15ev$12uh$1 digitalmars.com
Jan 24 2019
parent reply Neia Neutuladh <neia ikeran.org> writes:
On Fri, 25 Jan 2019 05:04:41 +0000, Mike Parker wrote:

 On Friday, 25 January 2019 at 03:52:23 UTC, Neia Neutuladh wrote:
 

 Credit to FeepingCreature for inventing this 5-10 years ago.


 
 2007 it seems, assuming FeepingCreature == downs:
 
 https://forum.dlang.org/post/fg15ev$12uh$1 digitalmars.com


Apologies for the misattribution, and thank you for correcting me.
Jan 24 2019
parent reply Mike Parker <aldacron gmail.com> writes:
On Friday, 25 January 2019 at 05:20:37 UTC, Neia Neutuladh wrote:

 On Fri, 25 Jan 2019 05:04:41 +0000, Mike Parker wrote:

 On Friday, 25 January 2019 at 03:52:23 UTC, Neia Neutuladh 
 wrote:
 

 Credit to FeepingCreature for inventing this 5-10 years ago.


 
 2007 it seems, assuming FeepingCreature == downs:
 
 https://forum.dlang.org/post/fg15ev$12uh$1 digitalmars.com


 Apologies for the misattribution, and thank you for correcting 
 me.


I wasn't correcting, but genuinely curious if it was the same 
person :-)
Jan 25 2019
parent Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
On Friday, 25 January 2019 at 08:51:55 UTC, Mike Parker wrote:

 On Friday, 25 January 2019 at 05:20:37 UTC, Neia Neutuladh 
 wrote:

 On Fri, 25 Jan 2019 05:04:41 +0000, Mike Parker wrote:

 On Friday, 25 January 2019 at 03:52:23 UTC, Neia Neutuladh 
 wrote:
 

 Credit to FeepingCreature for inventing this 5-10 years ago.


 
 2007 it seems, assuming FeepingCreature == downs:
 
 https://forum.dlang.org/post/fg15ev$12uh$1 digitalmars.com


 Apologies for the misattribution, and thank you for correcting 
 me.


 I wasn't correcting, but genuinely curious if it was the same 
 person :-)


 From https://forum.dlang.org/post/imqv4k$7kv$2 digitalmars.com:

On Monday, 28 March 2011 at 21:38:29 UTC, FeepingCreature wrote:

 I was d|owns but that name was stupid.


--
   Simen
Jan 25 2019
prev sibling parent bauss <jj_1337 live.dk> writes:
On Friday, 25 January 2019 at 03:52:23 UTC, Neia Neutuladh wrote:

 On Fri, 25 Jan 2019 03:45:36 +0000, Jonathan Levi wrote:

 I know this was not an intentional feature of d, but it is a 
 cool quirk.
 
 If you want to use a function that takes two arguments like a 
 infix binary operator (similar to the back ticks in Haskell 
 "`fun`") you can but a "." before and a "=" after.
 
      c = (a .fun= b);


 Consider also:

 struct Operator(alias fn) if (Parameters!fn.length == 2)
 {
     Curry opBinaryRight(string op)(Parameters!fn[0] arg) if (op 
 == "/")
     {
         return Curry(arg);
     }
     struct Curry
     {
         Parameters!fn[0] arg;
         auto opBinaryRight(string op)(Parameters!fn[1] arg2) if 
 (op == "/")
         {
             return fn(arg, arg2);
         }
     }
 }

 To use it:

 alias min = Operator!((a, b) => a < b ? a : b);
 writeln(1 /min/ 2);

 Credit to FeepingCreature for inventing this 5-10 years ago.


Now that's a hack I can support.
Jan 25 2019