Limit a generic type argument only to be a numeric type

Question

I am making a class, class numToBin <T>, and I need to make sure that T is a numeric value (Ex., Float, Double, Int, Long, UInt, Ulong, byte, short, BigInteger). I have seen a lot of posts asking the same question, but they are all a couple of years old.

My question is: Have there been any changes to the language to allow it now? Currently I have:

class numToBin <T>
    where T : struct, IEquatable<T>, IFormattable, IComparable, IComparable<T>

But something like T a = 0; doesn't work.

"has there been any changes to the language to allow it now?" No. — spender, Jun 14 '17 at 23:33
Could you link an answer or two that you think is out of date? — Sergey Kalinichenko, Jun 14 '17 at 23:33
https://stackoverflow.com/questions/1267902/generics-where-t-is-a-number https://stackoverflow.com/questions/3329576/generic-constraint-to-match-numeric-types https://stackoverflow.com/questions/2645301/generics-that-restricts-the-types-to-int-double-long Just some examples... — Optimistic Peach, Jun 15 '17 at 01:13
I updated the title of your question to more clearly describe what you were trying to do. I fixed the formatting, a few minor grammar and punctuation errors, and corrected your capitalization. I also turned the snippet of your existing code into a cleaner, neatly-indented, more-readable form. — Sean Werkema, Jun 16 '17 at 13:08

score 1 · Accepted Answer · answered Jun 14 '17 at 23:32

1

No, there is still no generic type constraint for a "numeric" type.

To get your T a = 0 specifically you can just use T a = default(T). The default of all numeric types is 0.

answered Jun 14 '17 at 23:32

BradleyDotNET

60,462
10
96
117

Ok, then how would one do a += 2 for example? – Optimistic Peach Jun 15 '17 at 01:12
@OptimisticPeach You can't. There is no numeric interface or constraint. – BradleyDotNET Jun 15 '17 at 04:00
To check for each of the types could I just do `if(default(T) == 0)`? – Optimistic Peach Jun 16 '17 at 23:03
@OptimisticPeach I'm guessing not, the compiler will think you are comparing an object to an int (checked in interactive window). – BradleyDotNET Jun 16 '17 at 23:08
@BradlryDotNet Ok, thanks. I will implement a method to check if it is numeric – Optimistic Peach Jun 16 '17 at 23:15

awiebe · Answer 2 · 2017-06-16T01:16:57.420

0

In the constructor of your class, perform type inspection to match the applicable types. If it fails throw an InvalidCastException or InvalidArgumentException.

Type t = typeof(T);
bool good = (t == typeof(int)) || (t == typeof(long))|| //...
if(!good)
 //die

edited Jun 16 '17 at 01:16

answered Jun 15 '17 at 05:43

awiebe

3,758
4
22
33

Ok, but if i do `Type[] types = { typeof(double) ....}` then, `(types[2]) a` doesn't really work, neither does `a+=1` – Optimistic Peach Jun 15 '17 at 17:21
The list of numeric primitives isn't very long, just check all of them. – awiebe Jun 16 '17 at 01:14

Limit a generic type argument only to be a numeric type

2 Answers2