On May 6, 2011, at 4:41 PM, MRAB wrote:
On 06/05/2011 23:51, Cameron Simpson wrote:
On 06May2011 15:40, Ethan Furman<ethan@stoneleaf.us> wrote: | Bruce Leban wrote: |>Is _ just ignored in numbers or are there more complex rules? |> |> * 1_2345_6789 (can I use groups of other sizes instead?) |> * 1_2_3_4_5 (ditto) |> * 1_234_6789 (do all the groups need to be the same size?) |> * 1_ (must the _ only be in between 2 digits?) |> * 1__234 (what about multiple _s?) |> * 9.876_543_210 (can it be used to the right of the decimal point?) |> * 0xFEFF_0042 (can it be used in hex, octal or binary numbers?) |> * int('123_456') (do other functions accept this syntax too?) | | I would say it's ignored. Have the rule be something like | number_string.replace('_',''). | | The only wrinkle is that currently '_1' is usable name, and that | should probably be disallowed if the above change took place. | | I'm +1 on the idea.
Personally I'm be for ignoring the _ also, save that I would forbid it at the start or end, so no _1 or 1_.
And I would permit it in hex code etc.
I'm +0.5, myself.
As far as I remember, Ada also permits it, but has the rule that it can occur only between digits. If we follow that, then:
1_2345_6789 => Yes 1_2_3_4_5 => Yes 1_234_6789 => Yes 1_ => No _1 => No 1__234 => No 9.876_543_210 => Yes 9._876_543_210 => No 9_.876_543_210 => No 0xFEFF_0042 => Yes int('123_456') => Yes
Java 7 also adds this feature. Its rules: You can place underscores only between digits; you cannot place underscores in the following places: • At the beginning or end of a number • Adjacent to a decimal point in a floating point literal • Prior to an F or L suffix • In positions where a string of digits is expected The following examples demonstrate valid and invalid underscore placements in numeric literals: float pi1 = 3_.1415F; // Invalid; cannot put underscores adjacent to a decimal point float pi2 = 3._1415F; // Invalid; cannot put underscores adjacent to a decimal point long socialSecurityNumber1 = 999_99_9999_L; // Invalid; cannot put underscores prior to an L suffix int x1 = _52; // This is an identifier, not a numeric literal int x2 = 5_2; // OK (decimal literal) int x3 = 52_; // Invalid; cannot put underscores at the end of a literal int x4 = 5_______2; // OK (decimal literal) int x5 = 0_x52; // Invalid; cannot put underscores in the 0x radix prefix int x6 = 0x_52; // Invalid; cannot put underscores at the beginning of a number int x7 = 0x5_2; // OK (hexadecimal literal) int x8 = 0x52_; // Invalid; cannot put underscores at the end of a number int x9 = 0_52; // OK (octal literal) int x10 = 05_2; // OK (octal literal) int x11 = 052_; // Invalid; cannot put underscores at the end of a number (From http://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html ) -- Philip Jenvey