how to define infix function
Simen Kjærås
simen.kjaras at gmail.com
Sat Jun 2 23:17:48 UTC 2018
On Saturday, 2 June 2018 at 22:09:49 UTC, Neia Neutuladh wrote:
> On Saturday, 2 June 2018 at 21:44:39 UTC, greatsam4sure wrote:
>> Sorry for the typo
>>
>> is it possible to define infix function in D
>>
>> 3.min(5)// 3: where min is a function, works in D
>> 3 min 5 // does not work.
>>
>> thanks in advance
>
> This is a horrible abuse of D's operator overloading discovered
> by FeepingCreature in the distant past.
>
> You have to delimit your custom infix operator with slashes;
> you can't make `3 min 5` work, but you can make `3 /min/ 5`
> work.
>
> Observe:
>
> struct Min
> {
> MinIntermediate!T opBinaryRight(string op, T)(T value) if
> (op == "/")
> {
> return MinIntermediate!T(value);
> }
> }
> struct MinIntermediate(T)
> {
> T value;
> T opBinary(string op, T)(T value2) if (op == "/")
> {
> if (value < value2) return value;
> return value2;
> }
> }
> Min min;
> void main()
> {
> writeln(1 /min/ 2);
> }
And of course, this can be generalized:
struct Operator(alias fn, string operator = "/")
{
static auto opBinaryRight(string op : operator, T...)(T
value1)
{
struct Result
{
auto opBinary(string op : operator, U...)(U value2)
if (__traits(compiles, fn(value1, value2)))
{
return fn(value1, value2);
}
}
Result result;
return result;
}
}
unittest
{
import std.algorithm.comparison;
alias min = Operator!(std.algorithm.comparison.min);
assert(1 /min/ 3 == 1);
}
Note also the use of static opBinaryRight, allowing one to eschew
the 'min' variable.
All of this said, I would suggest not using this in prod - it's a
neat trick that shows off some of D's power, but I don't see a
case where this would be easier to understand than a
straightforward function call.
--
Simen
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