digitalmars.D.learn - Array-wise expressions and range checking
- Alexander (26/26) Jun 16 2013 Hello,
- Jonathan M Davis (8/41) Jun 16 2013 Yeah, but as you failed to set any of c's elements to anything first, an...
- Alexander (4/51) Jun 16 2013 Opened the issue
Hello, I'm reading "The D programming language", part "4.1.7 Array-wise Expressions". It states that "The effect of an array-wise expression is that of a loop assigning each element of the left-hand side in turn with the corresponding index of the right-hand side. For example, the assignment auto a = [1.0, 2.5, 3.6]; auto b = [4.5, 5.5, 1.4]; auto c = new double[3]; c[] += 4 * a[] + b[]; is the same as foreach (i; 0 .. c.length) { c[i] += 4 * a[i] + b[i]; }" So I assume that the following code should generate runtime exception during evaluation of c[2] = b[2] + a[2], but it doesn't happen. auto b = [1, 2]; auto a = [2, 3, 4]; int c [] = new int[3]; c[] = b[] + a[]; return c; Is it an intended behaviour or a compiler bug?
Jun 16 2013
On Sunday, June 16, 2013 11:09:27 Alexander wrote:Hello, I'm reading "The D programming language", part "4.1.7 Array-wise Expressions". It states that "The effect of an array-wise expression is that of a loop assigning each element of the left-hand side in turn with the corresponding index of the right-hand side. For example, the assignment auto a = [1.0, 2.5, 3.6]; auto b = [4.5, 5.5, 1.4]; auto c = new double[3]; c[] += 4 * a[] + b[]; is the same as foreach (i; 0 .. c.length) { c[i] += 4 * a[i] + b[i]; }"Yeah, but as you failed to set any of c's elements to anything first, and they're default initialized to NaN, and all math done on NaN results in NaN, so none of c's elements will have changed in your example.So I assume that the following code should generate runtime exception during evaluation of c[2] = b[2] + a[2], but it doesn't happen. auto b = [1, 2]; auto a = [2, 3, 4]; int c [] = new int[3]; c[] = b[] + a[]; return c; Is it an intended behaviour or a compiler bug?That does look like a compiler bug. It should throw a RangeError, because a and b have different lengths, but it isn't. Please report it: http://d.puremagic.com/issues - Jonathan M Davis
Jun 16 2013
Opened the issue http://d.puremagic.com/issues/show_bug.cgi?id=10384 Thank you! On Sunday, 16 June 2013 at 09:35:23 UTC, Jonathan M Davis wrote:On Sunday, June 16, 2013 11:09:27 Alexander wrote:Hello, I'm reading "The D programming language", part "4.1.7 Array-wise Expressions". It states that "The effect of an array-wise expression is that of a loop assigning each element of the left-hand side in turn with the corresponding index of the right-hand side. For example, the assignment auto a = [1.0, 2.5, 3.6]; auto b = [4.5, 5.5, 1.4]; auto c = new double[3]; c[] += 4 * a[] + b[]; is the same as foreach (i; 0 .. c.length) { c[i] += 4 * a[i] + b[i]; }"Yeah, but as you failed to set any of c's elements to anything first, and they're default initialized to NaN, and all math done on NaN results in NaN, so none of c's elements will have changed in your example.So I assume that the following code should generate runtime exception during evaluation of c[2] = b[2] + a[2], but it doesn't happen. auto b = [1, 2]; auto a = [2, 3, 4]; int c [] = new int[3]; c[] = b[] + a[]; return c; Is it an intended behaviour or a compiler bug?That does look like a compiler bug. It should throw a RangeError, because a and b have different lengths, but it isn't. Please report it: http://d.puremagic.com/issues - Jonathan M Davis
Jun 16 2013