Is there any restriction for writing property names C#

Question

I've written a class definition like

 public class Item
        {
            public double? 30dhi { get; set; }
            public double? 30dlo { get; set; }
            public double? 7dhi { get; set; }
            public double? 7dlo { get; set; }
        }

Why it's not allowing me to add properties having alphanumeric keys The error is like below

invalid token '30d' for class , struct or interface member declaration

Use textual names like MonthHigh or WeekLow, or not so good in my eyes Lo7d, Hi30d — holroy, Jul 13 '15 at 05:59
@holroy: "Month" and "30 day" aren't the same thing though. I agree the current names aren't good, but I wouldn't change "30 day" to "month". — Jon Skeet, Jul 13 '15 at 06:02
@M.kazemAkhgary: perhaps downvoters feel that a question the answer to which is in TFM, "does not show any research effort" (one of the explicit reasons stated for downvotes). — Peter Duniho, Jul 13 '15 at 06:03
Note that the question of which this is a duplicate is specifically asking about class names, but the rules are the same as for property names; that question has an extensive discussion the rules for identifiers in C#, including at least two answers that are nearly identical in content to the one provided below. — Peter Duniho, Jul 13 '15 at 06:05
@jonskeet, I know 30 days are not always a month, but in some contexts that is what it is used for... — holroy, Jul 13 '15 at 06:05
@holroy: In *those* cases, I would agree - but why would you *assume* that the OP is using "30d" incorrectly, and suggest the change? — Jon Skeet, Jul 13 '15 at 06:06
@jonskeet, I was merely indicating alternative names to avoid starting the names with numbers which your answer correctly states is illegal. Suggested MonthHigh to get OP thinking in a different way, but still credit him to choose proper names. And most, but not all, times when I see 7 and 30 the context often is week and month. — holroy, Jul 13 '15 at 06:16
@holroy: Well, I think that was somewhat misleading - it would have been more useful IMO to think of what the OP should use if they really *do* mean 30 days. `ThirtyDayHigh`? (I have the opposite experience to you - we always *do* mean 30 days rather than 1 month...) — Jon Skeet, Jul 13 '15 at 06:18
@jonskeet, point taken, will try to be clearer in the future — holroy, Jul 13 '15 at 06:19

score 9 · Accepted Answer · edited Jun 20 '20 at 09:12

Why it's not allowing me to add properties having alphanumeric keys

A property name has to be an identifier. Identifiers in C# can't start with a digit. You can have a digit after the first character, but not as the first character.

See section 2.4.2 of the C# 5 specification for the precise details of what is allowed for an identifier. The full grammar is too long to post here usefully, but the crucial part is:

identifier-or-keyword:
   identifier-start-character identifier-part-characters_opt

identifier-start-character:
  letter-character
  _ (the underscore character U+005F)

identifier-part-characters:
  identifier-part-character
  identifier-part-characters identifier-part-character

identifier-part-character:
  letter-character
  decimal-digit-character
  connecting-character
  combining-character
  formatting-character

letter-character:
  A Unicode character of classes Lu, Ll, Lt, Lm, Lo, or Nl
  A unicode-escape-sequence representing a character of classes Lu, Ll, Lt, Lm, Lo, or Nl

Note that the example of 30d is a great one for why it's not allowed - that's actually a numeric literal, of the value 30 and type double. (You've actually got 30dhi of course, but the parser has parsed 30d as a token.)

that dear that helped . i missed it :) – Mani Jul 13 '15 at 06:22 — Mani, Jul 13 '15 at 06:22

Is there any restriction for writing property names C#

1 Answers1