Template function type inference with default arguments

ixid via Digitalmars-d-learn digitalmars-d-learn at puremagic.com
Sat Jan 3 16:22:00 PST 2015


Why don't templates take a type from the default argument if 
nothing else is supplied? It would be useful to be able to use an 
enum to set a default.

enum MAX = 1_000;

auto sieve(T)(T max = MAX) {
	import std.bitmanip : BitArray;
	BitArray n;
	n.length = max;
	T[] primes = [2];

	for(T i = 3; i < max; i += 2)
		if(n[i] == 0) {
			primes ~= i;
			for(T j = i + i; j < max; j += i)
				n[j] = 1;
		}

	return primes;
}

Changing the type to T = typeof(MAX) works but feels 
unnecessarily clunky and out of step with how templates normally 
operate when supplied with an argument.


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