## 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" <rride.a gmail.com> writes:
```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
Jonathan M Davis <jmdavisProg gmx.com> writes:
```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
"Alexander" <rride.a gmail.com> writes:
```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