objc-nsdate-formatter

When NSDateFormatter is used to convert an NSDate type to a String type, the user can specify a custom format string. Certain format specifiers are undesirable despite being legal. See http://www.unicode.org/reports/tr35/tr35-dates.html#Date_Format_Patterns for all legal date patterns.

This checker reports as warnings the following string patterns in a date format specifier:

  1. yyyy + ww : Calendar year specified with week of a week year (unless YYYY is also specified).

    • Example 1: Input Date: 29 December 2014 ; Format String: yyyy-ww;
      Output string: 2014-01 (Wrong because it’s not the first week of 2014)
    • Example 2: Input Date: 29 December 2014 ; Format String: dd-MM-yyyy (ww-YYYY);
      Output string: 29-12-2014 (01-2015) (This is correct)
  2. F without ee/EE : Numeric day of week in a month without actual day.

    • Example: Input Date: 29 December 2014 ; Format String: F-MM;
      Output string: 5-12 (Wrong because it reads as 5th ___ of Dec in English)
  3. F without MM : Numeric day of week in a month without month.

    • Example: Input Date: 29 December 2014 ; Format String: F-EE
      Output string: 5-Mon (Wrong because it reads as 5th Mon of ___ in English)
  4. WW without MM : Week of the month without the month.

    • Example: Input Date: 29 December 2014 ; Format String: WW-yyyy
      Output string: 05-2014 (Wrong because it reads as 5th Week of ___ in English)
  5. YYYY + QQ : Week year specified with quarter of normal year (unless yyyy is also specified).

    • Example 1: Input Date: 29 December 2014 ; Format String: YYYY-QQ
      Output string: 2015-04 (Wrong because it’s not the 4th quarter of 2015)
    • Example 2: Input Date: 29 December 2014 ; Format String: ww-YYYY (QQ-yyyy)
      Output string: 01-2015 (04-2014) (This is correct)
  6. YYYY + MM : Week year specified with Month of a calendar year (unless yyyy is also specified).

    • Example 1: Input Date: 29 December 2014 ; Format String: YYYY-MM
      Output string: 2015-12 (Wrong because it’s not the 12th month of 2015)
    • Example 2: Input Date: 29 December 2014 ; Format String: ww-YYYY (MM-yyyy)
      Output string: 01-2015 (12-2014) (This is correct)
  7. YYYY + DD : Week year with day of a calendar year (unless yyyy is also specified).

    • Example 1: Input Date: 29 December 2014 ; Format String: YYYY-DD
      Output string: 2015-363 (Wrong because it’s not the 363rd day of 2015)
    • Example 2: Input Date: 29 December 2014 ; Format String: ww-YYYY (DD-yyyy)
      Output string: 01-2015 (363-2014) (This is correct)
  8. YYYY + WW : Week year with week of a calendar year (unless yyyy is also specified).

    • Example 1: Input Date: 29 December 2014 ; Format String: YYYY-WW
      Output string: 2015-05 (Wrong because it’s not the 5th week of 2015)
    • Example 2: Input Date: 29 December 2014 ; Format String: ww-YYYY (WW-MM-yyyy)
      Output string: 01-2015 (05-12-2014) (This is correct)
  9. YYYY + F : Week year with day of week in a calendar month (unless yyyy is also specified).

    • Example 1: Input Date: 29 December 2014 ; Format String: YYYY-ww-F-EE
      Output string: 2015-01-5-Mon (Wrong because it’s not the 5th Monday of January in 2015)
    • Example 2: Input Date: 29 December 2014 ; Format String: ww-YYYY (F-EE-MM-yyyy)
      Output string: 01-2015 (5-Mon-12-2014) (This is correct)