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Feature #20404

closed

`2pi`

Added by mame (Yusuke Endoh) 8 months ago. Updated 8 months ago.

Status:
Rejected
Assignee:
-
Target version:
-
[ruby-core:117390]

Description

I propose a new Float literal: 2pi.

p 2pi  #=> 6.283185307179586 == 2 * Math::PI

I am not proposing 1pi, 3pi or 4pi. I do only 2pi. Because in most cases, all you need is 2pi. Any other multiple of pi is rarely needed.

I've got the statistics. GitHub code search revealed that more than 80% of the occurrences of n * Math::PI and Math::PI * n had n = 2. [1]

n n * Math::PI Math::PI * n sum %
0 48 1 49 1.4%
1 58 3 61 1.7%
2 2300 534 2834 80.4%
3 218 17 235 6.7%
4 200 23 223 6.3%
5 24 2 26 0.7%
6 41 3 44 1.2%
7 14 0 14 0.4%
8 6 2 8 0.2%
9 8 0 8 0.2%
10 17 0 17 0.5%
11 2 0 2 0.1%
12 2 0 2 0.1%

Here is the PIe chart

I know that a new constant name "Tau" is proposed (#4897, #17496). But notice: "2pi" and "Tau" have the same number of characters. Then, it is obvious that familiarity is better. In fact, 2 * Math::PI is 4 times more than Math::PI * 2, indicating that all programmers are copying "2pi" in their textbook.

The idea of 2pi came up regularly in chats among committers. The discussion quickly shifted to its generalization: should we treat 3e as 3 * Math::E, or even 42foo as 42 * foo? However, I noticed such a generalization is unnecessary because all we need is 2pi. Unneeded generalization is evil.

Here is a patch.

diff --git a/parse.y b/parse.y
index 55619273b8..93b16a16ac 100644
--- a/parse.y
+++ b/parse.y
@@ -10208,6 +10208,13 @@ parse_numeric(struct parser_params *p, int c)
             return set_number_literal(p, tINTEGER, suffix, 10, 0);
         }
     }
+    else if (c == '2' && peek(p, 'p') && peek_n(p, 'i', 1)) {
+        tokadd(p, c);
+        tokadd(p, nextc(p));
+        tokadd(p, nextc(p));
+        tokfix(p);
+        return set_number_literal(p, tFLOAT, 0, 0, 0);
+    }

     for (;;) {
         switch (c) {
diff --git a/ruby_parser.c b/ruby_parser.c
index 6d85a72c5b..3a6e0b5704 100644
--- a/ruby_parser.c
+++ b/ruby_parser.c
@@ -936,6 +936,9 @@ VALUE
 rb_node_float_literal_val(const NODE *n)
 {
     const rb_node_float_t *node = RNODE_FLOAT(n);
+    if (strcmp(node->val, "2pi") == 0) {
+        return DBL2NUM(2 * M_PI);
+    }
     double d = strtod(node->val, 0);
     if (node->minus) {
         d = -d;

       P I  
Happy a r l fool

[1] I used these queries: /[^.]\b2 ?\* ?Math::PI/ language:Ruby and /Math::PI *\* *2\b *[^.\/]/ language:Ruby


Related issues 1 (1 open0 closed)

Related to Ruby master - Feature #17496: Add constant Math::TAUOpenActions
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