Pass range to a function

[Ali Çehreli via Digitalmars-d-learn]

On 07/27/2017 02:16 PM, Chris wrote:

 > What is the value of `???` in the following program:

 > void categorize(??? toks) {
 >   foreach (t; toks) {
 >     writeln(t);
 >   }
 > }

The easiest solution is to make it a template (R is a suitable template 
variable name for a range type):

void categorize(R)(R toks) {
   foreach (t; toks) {
     writeln(t);
   }
}

Your function will work with any type that can be iterated with foreach 
and can be passed to writeln. However, you can use template constraints 
to limit its usage, document its usage, or produce better compilation 
errors when it's called with an incompatible type (the error message 
would point at the call site as opposed to the body of categorize):

import std.range;
import std.traits;

void categorize(R)(R toks)
if (isInputRange!R && isSomeString!(ElementType!R)) {
   foreach (t; toks) {
     writeln(t);
   }
}

Ali